This video introduces the basic concepts of working in a 3D environment in AutoCAD. Review Tutorial 3-3 for more information.
The biggest difference in switching from 2D drafing to 3D drafting is the addition of a 3rd axis - the "Z" axis. Another challenge is visualizing 3D objects on a 2D surface (your monitor).
Before you start digging into 3D, you should get very comfortable with these basic concepts and learn to change your view to get the best look at your 3D objects.