How can you join a digital repeater’s “talkgroup”?

In digital radio systems like DMR (Digital Mobile Radio), a 'talkgroup' is a way to organize users who share a digital channel, acting much like a virtual chat room. To hear and transmit to a specific talkgroup, you must program your radio with that group's assigned numerical ID. Because talkgroups are entirely a function of digital traffic routing, accessing them has nothing to do with the FCC or joining a physical repeater club. Signing your callsign after a courtesy tone is a practice used on analog repeaters, but it will not route your digital data to the correct talkgroup.