Basically how do Force Struggles work.
There is a Force Struggle at the end of every turn. Regardless of how many units there are, regardless of which units have focus tokens, or even if there are no units in play. There is always a Force Struggle at the end of each player's turn, no matter what's on the table.
The way you determine who wins is to simply check the following:
1) Do I have any units committed to the Force?
2) If so, are they Ready? (A unit is Ready only if it has zero focus tokens on it.)
If both of the above are true, then you count the Force icons on those units. This number will be your Force Total. You only count the icons on units that are committed to the Force and are Ready. You do not count the Force icons on any unit that is not committed to the Force, nor do you count the Force icons on a Committed unit that has 1 or more focus tokens on it. You also only count the Force icons on the unit itself; you never count Force icons on any enhancement that is attached to that unit.
It is possible to have a Force Total of zero, if:
1) You have no units in play
2) You have units in play, but none of them are committed to the Force
3) You have units committed to the Force, but they all have focus tokens on them.
Your opponent follows the same procedure, and whoever has more icons on his or her side wins, and the Balance of the Force marker will flip to match the winner's side (i.e., If the DS player wins, the marker will flip to the Dark Side). If it's a tie, the marker stays where it is.
Hope this helps!