If you’re going to start from scratch, just go with AutoCAD. It’s straightforward, really. As a beginner, you can pretty much handle all your 2D drafting with just a handful of basic commands.
For learning the ropes, honestly, look for that little orange Autodesk manual. It covers all the essential 2D fundamentals without any unnecessary fluff.
Now, if you have your heart set on 3D, do yourself a favor and put AutoCAD aside. Trying to model complex building structures in there is just unnecessarily tedious. You might want to try ArchiCAD if you want something relatively intuitive, or if you're feeling particularly masochistic, you could dive into Autodesk.
There’s also Home Depot's software out there, though I haven't actually sat down to test it myself yet.
