If you really want the newest edition of AISC's Manual of Steel Construction, wait until this autumn when the Load and Resistance Factor Design (LRFD) 3rd edition will be published. Otherwise, you'll be buying a book that will be obsolete in a few months.
In my opinion, the AISC Manual is not the easiest resource for a non-engineer to use to understand steel design calculations however. And if you want just the basics, LRFD might not be the way to go anyway. For simple applications, Allowable Stress Design (ASD) is sufficient and much easier for the inexperienced to grasp.
An introductory text like Ambrose's might be more what you're looking for. Or if you want a relatively simple introduction to LRFD, William Segui's "LRFD Steel Design" is a good one.