You control the yellow on the left. It indicates where you are to create your soldiers. You can move it up and down by pressing W and S or Up and Down Arrow Keys. To select different types of soldier use A and D or Left and Right Arrow Keys. When you have your preferred unit selected and he is ready, press the Spacebar to release him. Every 20 kills, you will get a charge where you can send out a line of 8 men. This indicated by a red arrow. Press Q to release a charge.

2 Player Mode.
Left Player:
W / S - Move Arrow Up and Down.
A / D - Select Unit.
Spacebar - Release Unit.

Right Player:
Up / Down Arrow Keys - Move Arrow Up and Down.
Left / Right Arrow Keys - Select Unit.
Enter Key - Release Unit.