If you are looking for guides or books to learn this specific version, several highly-rated resources remain available:
Before buying, confirm your hardware and OS can actually run this 15-year-old software:
Buying AutoCAD 2012 directly is no longer possible through Autodesk as it is a "legacy" version that has reached its end-of-life. However, you can still acquire it through specific alternative methods or buy a modern subscription that includes access to older versions.