Click the Synchro button and drag and drop a blue line from one thing to another.
If you join two waypoints belonging to different groups, the first group to arrive at that waypoint will wait there till the other one arrives at its waypoint. They both move on at the same time.
If it's a trigger and a waypoint, the group will wait until the trigger is fired.
If the trigger is type switch ... well I could go on for a bit yet but hit the tutes in the Editors Depot - Tutorials - Getting Started, its all there.