Hi agridude
When you group a trigger to a unit the trigger options will change a bit.
You can now select by whom / what in that group the trigger will be activated - vehicle, group leader, whole group, any group member.
I've never ever used synchronizing but I think the main idea about it is that it will do two things simutaniously.. or rather by if the other is activated then the other one will be also.
I think you can't group triggers to waypoints, you'd have to synchronize them. and also I think you can't synchronize a trigger to a unit.
please anyone correct this if I'm wrong.. just guessing here from faint memory.
group(F2) --- unit <--> trigger
synchronize(F5) --- trigger <--> waypoint