Starting in CAD, you can go many ways.
You need to decide if you want to use a more mainstream CAD package like Soliddworks or if you want to try one of the many freebe versions out on the web.
If you pick a freeby you will have to learn what everything does through trial and error or by reading the help files and asking a lot of questions on line.
If you know someone close who already knows and uses CAD they may be able to help you in a few ways.
Or you can go to TAFE or TECH whatever it is called and learn Inventor, which is another more main stream CAD.
However whichever way you eventually go you will find it so helpfull in every aspect.
I use either Inventor Pro 2012 or Solidworks Pro 2012 myself, as well as Mastercam X5, for my CAM work and Mach 3 for when I eventually get one of my mills converted to CNC.
I know this may not be all that much help but there are a million different views and everyone has their own opinion.