Organizing a formation is a total PitA.
However, grouping units together or dispersing them isn't so bad. To group units together, just drag+select the units you want in the new group and hit the G-hotkey. You get the menu. Click on the units you want to place within the group and hit the button with the arrows showing them coming together. (The other button is the one for separating a unit from a group.
To detach a unit from a group, click on the group and hit the G-hotkey. When the menu comes up, click on the unit and then the Detach button. It sometimes takes a few minutes for the units to detach, but they will.
Formation editor is such a PitA and ridiculous to use that I just don't bother.