PBEM games, or Play By EMail, utilize either direct email or posting on a Bulletin Board or Forum to inform the players of the status of the game. Battlestar Galactica PBEM is played on the Groups.io of the same name. In order to play you must have a Groups.io account and be a member of the BSG PBEM forum. You can find links to the appropriate sites below.
To sign up with Groups.io, go here.
To visit the Battlestar Galactica PBEM Forum, go here
I use GURPS rules primarily to resolve combat, situations where particular skills are required to determine a specific outcome. A knowledge of GURPS rules IS NOT needed to play the game, the mechanics are largely invisible to play. But if you are interested in learning more there are PDF files on the Forum that can be downloaded. These contain a basic outline of GURPS rules and are known as “GURPS Lite.”