Subtracting allows complex objects like a rectangle with a hole through it to be made.

Intersect is used for when 2 objects are drawn over each other and the part(s) where the objects overlapped are kept.

Union:

In this picture, I have 2 rectangles, a wedge and a cone:

Selected, the lines would appear like this:

Now that looks really messy doesn't it? To change this, select the union tool OR type “_union” then select all the objects:

Then we press ENTER. All these objects will become one big object:

Subtract:

In this picture, I have a normal rectangle:

Now I'm going to draw another one intersecting it:

I'm going to make a rectangle with a hole through it like a hole for a door. In order to do this I could draw a lots of rectangles or I could simply use the subtract tool. To do this, click on the subtract tool or type in “_subtract”.

There is a certain order you must select objects. Select the object you are going to subtract FROM, in this case the taller rectangle. Then you press ENTER. Now you select the object you are going to use to subtract, here it is the smaller rectangle. Then you press ENTER and you are left with this:

Intersect:

In this picture I have a sphere and a rectangle intersecting:

For some odd reason I want the part that is overlapping ONLY. To do this, select the intersect tool or type “_intersect”. I then select both objects and press ENTER and I'm left with this:

I hope you have learnt something from this tutorial!

Note: If you accidentally select the wrong object, you can unselect it by holding SHIFT and clicking on the selected object.