You player is highlighted with a small blue arrow over his head. Move it with arrowkeys left, right, up and down. You have three additional keys to run, pass and shoot:
Running key: keep it pressed to run. Default run key is 1.
Passing key: press it to pass when your player holds the ball. You will see a red bar growing in the bottom of the screen. The longer is the bar, the longer will be the pass. If you press it when you are away from the ball, your player will raise his arm and call for it! If you are playing as a goalkeeper, use it do dive and catch the ball. Default passing are 2 and 4 (high pass).
Shooting key: press it to shoot when you team is attacking and use it to sweep the ball when your team is defending. As for the passing key, you will see a blue bar. The longer is the bar, the strongest will be the shoot. Don't exagerate or you will miss the goal! Default shooting key is 3.
You can change keys anytime in the Settings page.