Let me add that you can also type in exact dimensions when you are drawing something. Say you want to create a rectangle that's 1.5 x 3.5 inches, you just start to draw it, then type "1.5, 3.5" sans quotes. If it comes out the wrong way, undo it (ctrl-z) and try again but reverse it so it goes "3.5,1.5". You can type dimensions as you are drawing (or pushing/pulling) or immediately after you release the mouse button after drawing something.
This is WAY easier than trying to draw it right by hand!