One of the ways to install additional software in the FreeBSD system is with ports. Here is a brief explanation on how to download the "ports tree" and install one of then (perl).
1. Use the portsnap command to download the ports tree into the local system:
portsnap fetch extract
2. The ports tree will be created under "/usr/ports/". Once it is populated with all the makefiles and patches, any of the ports can be installed by doing the following e.g. perl:
cd /usr/ports/lang/perl5.20/ && make install clean
3. At last, check whether the installation was successful: