About groups:
1: There wil lbe a number of circle icons over the bottom part of the interface. This is the group.
2: If you move a unit into the sovereign's area, or a group, or move the sovereign onto a group, that will form a new group.
3: To split up units in a group, click on them so there's a small 'up-arrow' on the unit(s) in question. (Shift-click for more than 1). Right clicking anywhere will tell them to leave.
4: Using escape to deselect the group may be useful, it's not allways responding too well to clicking again to toggle it off.
5: The skill Tridus mentions is 'organized' and I believe that may be the best skill in the game.
(It lets certain slow monsters still keep track with the boss.).