I`m a CAD draughtsman, I use AutoCAD all day long. I had no proper training when i started. I picked it up along the way, that was about 10 years ago now. 3D Cad would be different tho, thats alot harder to learn and do correctly.

Get a copy of AutoCad, and just have a play, and get a book, and you will pick it up quite quickly.