I'm having fun with this ScreenRecorder program.
Here is a demo of the dimensioning feature in Inventor. You really should watch the tutorial that Elgin mentions, but if you want a quick intro then.... I'd use the Ordinate Dimension set, choose your points and then right click and select "create". It's that simple. All the dimensions whould be the same as the part you made, and if you change your part, the drawing will update automatically.
