Explain the following Mesh construction techniques: box modelling; extrusion modelling; using common primitives, e.g. cubes, pyramids, cylinders, spheres.

Box modelling is when the user is able to locate the create section and make a box here you are able to edit the parameters and the amount of segments the box then has. this can be made very easily by dragging and propping in any of the perspectives.
Extrusion modelling is where the shape has been made and now it needs to be extended on one of its faces or vertices. By selecting extrude and inclining the amount it makes the shape extend and extrude in the selected area. 
Mesh's are multiple shapes together that may have been edited, placed together in order to form an overall shape.The definition of a spline is a 2D object with vertices and segments. Once made i was then able to edit the shape of the spline

Mesh Construction Using SplinesFirst I made a spline. To create this I clicked on the line tab, I created it in the top viewport. To create it you click and drag, to release you right click. 

I then clicked onto the vertex tab and clicked onto the middle dot and dragged it upwards on the z axis. So that it then looks like a triangle or the top of a roof.

When I had done that I then cloned that line by holding the shift key and dragging. When I released it a tab came up, I changed it to instance. I changed it to instance because if I want to change any of the lines in any way it will change the one that is duplicated in the same way.

I then deleted the clone I did and made another but this time I changed it to copy. I changed the colour to pink. I then made another clone and changed the colour to green so that I had 3 splines altogether. As these are copies I can change them all so that they look different. When I change them they wont all change the same to the one that has been changed.
I then made a surface, to do this I had to attach the three splines together. I clicked onto the attach function which is located on the right hand side in the command panel under Geometry. When all three splines have been selected I then turned off the attach button.

After this i used the cross section tool to join the splines together to create the base for my surface. After this i then used the modifier 'surface' tool. this then fills in the planes to create the surface.

I used the sub objects spline level and selected all the vertices. From here i was able to move them and then show the end result using the simple tool on the right hand side known as show end result. But, with only 3 vertices we don't have much definition in the shape. So we can change to besire which gives us a new level of curvature  but still not many due to lack of sub divisions.

In order to gain more control i added an edit poly modifier to control more, this then expands into vertex, edge, border, polygon and element. When dealing with a spline it is called a segment, but when dealing with a poly its called an edge. Border is a function that if a section has been cut out border then follows those edges and using the cap tool you are able to fill in the gap.

The element function is the whole object you are dealing with. After we applied a Mesh Smooth modifier, this smoothed out the shape and using the ireations tool i was able to decide by how much it would be smoothed out.
Now I was able too look back and see the progress made. First i made a line, then a surface, then an editable poly for more freedom and finally a mesh smooth. I was able to step backwards to line to control the splines but it gives us first a warning notice that the effects may be undesirable. Once OK was clicked you were able to move the vertices along thus breaking the surface. But if i grab two vertices together i can control it. When making another spline i can easily use the smooth and this edits the tangent in and out and can use besire to increase or decrease curvature.