The CVS distribution contains a number of subdirectories. In the course of a normal installation, you won't have to navigate among them, but if you want to go poking around in the sources, it's nice to know what each one does. Here they are:
contrib/ diff/ doc/ emx/ lib/ man/ os2/ src/ tools/ vms/ windows-NT/ zlib/
The majority of these can be ignored. The emx/, os2/, vms/, and windows-NT/ subdirectories all contain operating-system-specific source code, which you would only need if you're actually trying to debug a code-level problem in CVS (an unlikely situation, though not unheard of). The diff/ and zlib/ subdirectories contain CVS's internal implementations of the diff program and the GNU gzip compression library, respectively. (CVS uses the latter to reduce the number of bits it has to send over the network when accessing remote repositories.)
The contrib/ and tools/ subdirectories contain free third-party software meant to be used with CVS. In contrib/, you will find an assortment of small, specialized shell scripts (read contrib/README to find out what they do). The tools/ subdirectory used to contain contributed software, but now contains a README file, which says in part:
This subdirectory formerly contained tools that can be used with CVS. In particular, it used to contain a copy of pcl-cvs version 1.x. Pcl-cvs is an Emacs interface to CVS. If you are looking for pcl-cvs, we'd suggest pcl-cvs version 2.x, at: ftp://ftp.weird.com/pub/local/
The PCL-CVS package it's referring to is very handy, and I'll have more to say about it in Third-Party Tools.
The src/ and lib/ subdirectories contain the bulk of the CVS source code, which involves the CVS internals. The main data structures and commands are implemented in src/, whereas lib/ contains small code modules of general utility that CVS uses.
The man/ subdirectory contains the CVS man pages (intended for the Unix online manual system). When you ran make install, they were incorporated into your Unix system's regular man pages, so you can type
floss$ man cvs
and get a rather terse introduction and subcommand reference to CVS. Although useful as a quick reference, the man pages may not be as up to date or complete as the Cederqvist manual (see the next section); however, the man pages are more likely to be incomplete than actually wrong, if it's any comfort.