Polygonal Modelling
A polygon mesh is made up of vertices, edges and faces to help create a 3D Object. This type of modelling is usually done by using a primitive object such as a cube and then editing and modifying the object using tools which 3D programmer usually have programmed in already. Using these tools help create a more complex shape that still involves having the polygon mesh. Polygonal modelling is one of the most popular techniques when constructing 3D models which will be rendered for video games. To create more difficult and complex shapes using a simple primitives shape like a cube will consists off extruding and subdividing the shape to help create more edges, vertices and faces. The faces in Polygonal modelling usually consists off triangles, Quadrilaterals or other shapes similar to the polygon.
Primitive Modelling
Primitive modelling is modelling which is created by using the most basic shapes such as Cubes, pyramids, Cylinders and Spheres. These shapes are usually already Pre-Made in 3D programs although You can manually make the primitive shapes too. The main idea of using Primitive modelling is to use these primitive shapes to create new shapes and objects which can be complicated. Primitive is one of the most popular modelling techniques simply because it is the easiest and most effective technique. However Primitive modelling usually involves having to join primitive shapes together or subdividing a primitive shape which will increase the polygon count for example the more you extrude or create new shapes the more the vertices, faces and edges are in the modelling meaning that it takes a lot more memory which could get to much for real life rendering, Making it un-suitable for video games unlike the polygonal modelling technique.
Box Modelling
Box modelling is another technique used to construct a 3D model. This technique also involves using primitive shapes just like the primitive modelling technique. Although Box modelling has a progress off using the same steps repetitively until you are satisfied with the final model. The process included using tools which 3D modelling program already supply. These tools include extruding,sub divide and scale to help create more surfaces in the object so it can be manipulated and adjusted into a a different shape. Box modelling usually involves only using one primitive shape and then creating a object out of that one primitive shape by using the tools over and over till the shape is completed. This is effective because it only involves using one shape which makes it a lot less time consuming the artist to be more imaginative because this technique allows the artist to create a new, unique more detailed shape just by using a simple primitive shape.
Extruding: Exuding is usually used on faces, It basically creates a new face which you can push out. Extruding the object. For instance If I had a cube and extruded the top of the cube then another cube will extrude out the top of it.
Sub divide: Subdivision is a tool which splits faces and edges into a smaller piece by adding a new vertices. Doing this can create a smoother surface or allow the artist to move the new vertices to create a new shape.
Scale: Scale is basically resizing and scaling the object.
Extrusion modelling
In this method the artist will create a 2D shape which outlines the object for instance this can be created in Photoshop, illustrator, of an image or a drawing. The artist then uses another image of the same object but at a different angle and in a different frame/window in the 3D program. Once done the image is then usually 'traced' in the 3D modelling, covering it in a lot of polygons. Since this object is now covered in polygons it allows the artist to manipulate it to make changes and once ready the artist can extrude the polygons. Making the 2D trace of an object go into a 3D model. Extrusion Modelling technique is a advantage because It allows the artist to plan out the image and then import it into a 3D software which supports the file and then simply trace over the image and extrude it, Making it symmetrical.
Sketch Modelling
Sketch modelling is basically a technique which allows the artist to create 3D models as if they are making the object out of clay or mold, Allowing the artist to add more detail. Considering this is one of the main technique which allows the artist to add detail, it is a really popular technique for modelling character faces due to the amount of detail you can put into the face for instance you can put wrinkles and everything in the face. However games industry do not usually like using this technique because to use the sketch modelling technique, the artist usually starts out with a block so at the end of the character/Object their is a lot of polygons which can be to much for most software which can cause issues with the appearance of the character and the performance for example the software can get confused and to 'loaded' so it can cause lag.
3D Scanners
3D scanning is a quick way to generate objects our of real life. For instance the 3D scanner allows the user to scan any objects from real life.This allows the user to get a realistic Scan for 3D modeling for example if the user scanned a hand the hand will then be put into a virtual image which then the artist can use for modelling. Making it a lot easier to have real life scales of objects from real life, Making object as realistic as possible. however Because 3D printers are quite effective this technique isn't as popular as the previous techniques although they are still generally used by researchers and industry professionals.
Links
http://www.zwsoft.com/zw3d_forum/thread-3780-1-1.html
https://knowledge.autodesk.com/support/maya-lt/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/MayaLT/files/GUID-7941F97A-36E8-47FE-95D1-71412A3B3017-htm.html
https://en.wikipedia.org/wiki/3D_modeling
http://www.virtualaloft.com/3d_modeling/
http://dcdesign.wikidot.com/wiki:box-modelling
http://iceysandwich.blogspot.co.uk/2014/03/responsive-creature-modelling-modelling.html?view=flipcard
http://gadgetmix.com/3d-scanners-and-their-uses/
http://www.3ders.org/articles/20151209-best-3d-scanners-2015.html
Box Modelling
Box modelling is another technique used to construct a 3D model. This technique also involves using primitive shapes just like the primitive modelling technique. Although Box modelling has a progress off using the same steps repetitively until you are satisfied with the final model. The process included using tools which 3D modelling program already supply. These tools include extruding,sub divide and scale to help create more surfaces in the object so it can be manipulated and adjusted into a a different shape. Box modelling usually involves only using one primitive shape and then creating a object out of that one primitive shape by using the tools over and over till the shape is completed. This is effective because it only involves using one shape which makes it a lot less time consuming the artist to be more imaginative because this technique allows the artist to create a new, unique more detailed shape just by using a simple primitive shape. 
Extruding: Exuding is usually used on faces, It basically creates a new face which you can push out. Extruding the object. For instance If I had a cube and extruded the top of the cube then another cube will extrude out the top of it.
Sub divide: Subdivision is a tool which splits faces and edges into a smaller piece by adding a new vertices. Doing this can create a smoother surface or allow the artist to move the new vertices to create a new shape.
Scale: Scale is basically resizing and scaling the object.
Extrusion modelling
In this method the artist will create a 2D shape which outlines the object for instance this can be created in Photoshop, illustrator, of an image or a drawing. The artist then uses another image of the same object but at a different angle and in a different frame/window in the 3D program. Once done the image is then usually 'traced' in the 3D modelling, covering it in a lot of polygons. Since this object is now covered in polygons it allows the artist to manipulate it to make changes and once ready the artist can extrude the polygons. Making the 2D trace of an object go into a 3D model. Extrusion Modelling technique is a advantage because It allows the artist to plan out the image and then import it into a 3D software which supports the file and then simply trace over the image and extrude it, Making it symmetrical. Sketch Modelling
Sketch modelling is basically a technique which allows the artist to create 3D models as if they are making the object out of clay or mold, Allowing the artist to add more detail. Considering this is one of the main technique which allows the artist to add detail, it is a really popular technique for modelling character faces due to the amount of detail you can put into the face for instance you can put wrinkles and everything in the face. However games industry do not usually like using this technique because to use the sketch modelling technique, the artist usually starts out with a block so at the end of the character/Object their is a lot of polygons which can be to much for most software which can cause issues with the appearance of the character and the performance for example the software can get confused and to 'loaded' so it can cause lag.3D Scanners
3D scanning is a quick way to generate objects our of real life. For instance the 3D scanner allows the user to scan any objects from real life.This allows the user to get a realistic Scan for 3D modeling for example if the user scanned a hand the hand will then be put into a virtual image which then the artist can use for modelling. Making it a lot easier to have real life scales of objects from real life, Making object as realistic as possible. however Because 3D printers are quite effective this technique isn't as popular as the previous techniques although they are still generally used by researchers and industry professionals. 
Links
http://www.zwsoft.com/zw3d_forum/thread-3780-1-1.html
https://knowledge.autodesk.com/support/maya-lt/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/MayaLT/files/GUID-7941F97A-36E8-47FE-95D1-71412A3B3017-htm.html
https://en.wikipedia.org/wiki/3D_modeling
http://www.virtualaloft.com/3d_modeling/
http://dcdesign.wikidot.com/wiki:box-modelling
http://iceysandwich.blogspot.co.uk/2014/03/responsive-creature-modelling-modelling.html?view=flipcard
http://gadgetmix.com/3d-scanners-and-their-uses/
http://www.3ders.org/articles/20151209-best-3d-scanners-2015.html