A "standard" perl install from the source at CPAN should work like this:

# untar source, cd into the directory
./Configure
# answer bunch of questions (defaults are usually good)
make
make test
# change to root
make install
[download]

However, FreeBSD has its own ports system that you should probably use instead if you want to install the default perl interpreter for that system.

I'm not at all familiar with BSD ports, but according to the link i posted above, you should "rerun use.perl port" after you 've done whatever you did to install perl.

this link seems to describe the same procedure.