My long-time friend and colleague Brian Tanaka has written a new eBook "Take Control of Permissions in Mac OS X" that provides a bunch of help for the average Mac user in dealing with the often mysterious subject of "permissions" and "ownership" of files and folders in Mac OS X.
Permissions and ownership of files and folders are a tough subject.
Part of the reason, I think, is that there isn't a really good physical-world analogy - objects in the physical world don't have -rwxr-xr-x attached to them, so it's a pretty alien concept - in the physical world, if you can touch it you can write on it, now maybe you shouldn't write on it, because of laws, social custom, etc. but there are no attached permission settings, and no operating system to enforce permissions. Ownership is an easier concept for people to grasp, because of the extensive real-world analogs.
Brians' eBook is a good, searchable, handy guide to dealing with these issues, and it's only ten bucks. You do not need to know, or care about Unix to benefit from his guide, and even experienced users will find stuff they didn't know - for example what "Repair Permissions" and "Ignore Ownership" actually do.
If you want to really dive into learning the Unix layer of Mac OS X, and can handle a higher price-tag, and dealing with a paper book, then I recommend my book (shameless plug, I know) "Unix for Mac OS X Tiger", but to focus on just Permissions and Ownership, Brians' book is a fine place to start.