That is a typical way to set up a directory tree that is meant to be compiled from source, yes. If you are just trying to look at the source, lib/ is likely the directory you want.

They are set up that to be consistent: When it comes to Perl modules, you can run Makefile.PL to generate the, erm, makefile (which is basically a file containing instructions to the C compiler as to what it's job is going to be). You can then use the make command to actually build it.

See here for some more info about installing stuff from source on *nix.

And no, you don't have to understand ALL of how it works to be able to use it. And yes, there are automated ways of installing Perl modules :)