Autodesk AutoCAD is considered the benchmark of all general non trade-specific CAD applications. It's also the most expensive, which most think is ridiculous but others see it as a small price to pay for what you get. This is, of course, related to how much use you get out of it.
Anyways, you do have alternatives and options. First option, download the 30 day trial of AutoCAD LT which an official Autodesk product. If in 30 days you can see the usefulness, then you'll have to shell out up to $1,200 for this version. Vanilla AutoCAD would be $4k I believe. This is if you wanted to stick with Autodesk.
Another alternative would be a much less expensive option for a licensed CAD application, including support. Bentey Products, or something like TurboCAD, for example.
Or, you can try some free versions with only a registration as the key to a full CAD application. http://www.caddit.net/progecad/smart.php has ProgeCAD Smart, which is a free CAD application for personal use that is strikingly similar to Autodesk's AutoCAD.
Now, in getting yourself trained, that's where the help file, and sites such as this one will come in real handy. Stick with us and you'll get plenty of support from real world designers all day every day. Hope this helps some.