What you were downloading was probably the rules which tell a system how to put together a port. Instead of downloading this file, quite often the easiest way to get a port is with the "pkg_add" command. Open a terminal window and type
pkg_add -r -v name_of_port
Alternatively, if you want to compile ports from scratch, you'll want to download the Ports tree, that is the rules that determine what ports are available and how theyare installed.
You might want to read this manual page on the subject