CVS is a version control system for source code. Its not important whether or not you actually use it to control your site-local modifications. However, even if you don't, it's still important that you put your modifications under a directory in $FBHOME/cvs.
At this point, you already have a directory named cvs underneath your $FBHOME directory. Further, that directory already has under it many directories which hold the ‘general’ files.
What you want to do now is make a directory that holds the ‘local’ files. The included maintenance tools look for your files in a directory beside fb named local, but local can actually be a symlink to your working directory.
In $FBHOME/bin there' a tool named cvsreport.pl which manages (among other things) merging together the general files and your site-local files into the live area under $FBHOME.
The command you'll need most of the time is:
$ cvsreport.pl -c -s
-c is short for --cvsonly (only copies from the cvs directory back to the live area, not vice-versa) and -s is short for --sync (which means actually do the copying, don't just print out what it would've done, which is the default without -s).
Example 3.2. Overriding index.bml:
So, say you want to override the provided htdocs/index.bml file. Create the htdocs directory under $FBHOME/cvs/local and put a index.bml file in it, then run cvsreport.pl -c -s and you're set.
More commonly, you'll be adding new files, rather than replacing provided ones. Ideally, you should never really need to replace files, since you should already be able to change all the text, images, and layout of any given page. Replacing a file would mean duplicating functionality, and that's bad.
One popular strategy with the general code libraries is to look for a similarly named file with -local in it and load that also. That way you inherit all the functionality that's provided, and change only what you want. When files in the main repository change, you don't have to update right away… you can change things later if you want, or keep the newly added stuff as it was given to you.