I will be taking a CADD course next year when I am a sophomore. I am only 15 and only want it for small things.
But you are currently enrolled, in High School I assume? If so that could really work to your advantage. Most of the big companies will allow students to download free, legit versions of their software.
For 3D I would start with solid works. It is probably the simplest most commonly used commercial program out there. A bunch of online tutorials are available. Outside of that, Inventor, NX/Unigraphics, Catia, Pro Engineer are all good, and highly used, but start to get a bit more complicated for self learning in short time. Honestly if you can get one down you will be able to pick the others up pretty fast.
If you get into mechanical engineering or the like, it is sorta assumed these days that you know auto cad 2D. Basically electronic pencil and paper.