Let's say you are group Alpha, and group Bravo is waiting on standby in a town nearby, or some trees off in the distance. Give the leader of group Bravo a move waypoint right where he is standing and another where you want Bravo to go when called by the radio. In the condition of the first waypoint, change the word true to help. Next, make a trigger and click the activation box and choose radio Alpha. In the on activation of the trigger put-
help=true; leader Bravo sidechat "We're on the way!"
This will release Bravo from the first waypoint and they'll come a runnin. For the sidechat to work, the group names need to be specified in the leaders initialization, ie... Bravo = group this