While I can appreciate your frustration with the index (and agree to a certain extent), some of your frustration here is misplaced. In general, the book is a good reference for building Eclipse plugins, but it does make one or two crucial assumptions, if you are going to use it in that manner. If you are going to use it as an ad-hoc reference, you need to have either a) read the book or b) be somewhat familiar with Eclipse plugin development and terminology. If you are unfamiliar with the basic terminology (e.g., your earlier comment about not knowing what an "action" is), then you won't have a good basis for finding anything in the index.
For example, had you known that the general term for the thing you wanted to filer was "action", then looking in the index under "Actions" would have lead you to "filtering and enablement" right away. Likewise, your comment about "RFWS". There are lots of index entries dealing with RFWS - either under the appropriate topic area (like "Views") or gathered together under "Ready for WebSphere Studio (RFWS)". Granted, there should be a specific "RFWS - See Ready for WebSphere Studio" entry in the index, but the "RFWS" term is introduced right up front in the book's Preface. At minimum, you should probably read the Preface and Chapters 2 & 3 just so that you can ground yourself in the basics before trying to hunt through the index.
This book is also not an "Encyclopedia of Eclipse Plugin Development" that covers all possible topics (we would need a couple more volumes for that). It is primarily a generic book on plugin development rather than a specific guide on building specific types of plugins. We don't, for example, go into detail on using the GEF, EMF or JDT libraries as those could easily expand into books all by themselves (and in the case of EMF, it did). Thus, this book deals primarily with generic IResources and IProjects rather than the specifics of the JDT and IJavaProjects.