You can't "open" ports. Ports are considered "open" when a response is received from a program or daemon listening on that port (most often, this is inet.d).
The idea, is to close them, where are there listening ports that leave you vunerable.
To open a port, launch an app or daemon, and configure it to listen on that port. This will not open it to anything, simply the service that is listening (ssh, http, X, etc...)