I think that, as soon as you've gained a fundamental introduction into the RapidWeaver interface and how the program works, you will want to get this add-on feature called "Stacks." Stacks does not replace RapidWeaver; Stacks enhances the native power of RapidWeaver. While RapidWeaver provides a wide variety of built-in page types, it limits you to laying out objects on its pages to the native RapidWeaver way. Also, RapidWeaver by itself cannot accomplish a lot of neat tricks that might require the skills of an experienced programmer.
Stacks solves those limitations by creating a special type of page in the Stacks format onto which you can drag other specially designed stacks by a myriad of third party developers, each one set to out-do the other by coming up with clever, useful features that extend the power of RapidWeaver by letting the program—through these individual stacks laid out upon a Stacks page—do things beyond it original conception. In other words, RapidWeaver is the big playground that you need to develop the website, while Stacks is the gateway foundation you need in order to bring other stacks designed to perform specific functions that extend the power of RapidWeaver way beyond its borders.
For example, there is no easy way to build tables in RapidWeaver, but there are a few stacks that do the job quite well. RapidWeaver can give you a photo gallery page that is quite adequate, but basic; there are stacks which do this much better, adding slide show features beyond what RW itself can do. With Stacks, you can create an outline, expand your menu options, add light boxes, lay out your pages easier and cleaner, and do a whole lot more than you can do with RapidWeaver alone.
First, get RapidWeaver, then get Stacks. Then browse the add-ons section at RealMac Software to see all you can do. Then get a grip on your credit card. While Stacks and most stacks and relatively inexpensive, you could get addicted to building up your collection once you see the power of using Stacks in your designs.