I'm assuming your OS is Windows, so you can try these links for a bit of information on using the Ping
As it suggests in those guides, you need to know the IP address of the system you are trying to ping.
If you are simply trying to find out your ping to a game server - that is usually displayed in the in-game browser when you 'Refresh List'. The lower the ping, the better your gaming experience will be on line.
Alternatively, you can download game browser utilities like All Seeing Eye
which list game servers along with their pings. You can also re-ping servers individually using that program.