Creating Groups in tactical combat

[Growltigga]

Apologies, another newby question.

How do you set up Groups of ships for tactical combat? I have worked out how to clear all assignments for all Groups (tricky one that) from the menu, but I would like to be able to assign a fleet at the start of tactical combat into various smaller sub-Groups, each with different formations etc.

I have also hit this problem when trying to invade a planet. I have 3 troop transports loaded to the gills with my finest troops but because I have disabled all group assignments, when I move then to the planet, each troopship drops its complement individually and naturally, gets whomped by the defenders.

Help?