In Firefight you control the commander of your team. Here is a basic overview of how you control the commander.
Aiming: Touch and drag anywhere on the right side of the screen to aim. Aiming at an enemy soldier in range will automatically fire at them.
Movement: Touch and drag anywhere on the left side of the screen to move. Once you tap down on the left side of the screen you will see a virtual analog stick appear.
Hint: If you are not moving your commander will crouch
Reload: If you have used some of your ammo in your clip and you want to reload, tap anywhere along the clip bar at the bottom of your screen in game.
Hint: If you crouch you will reload quicker