We often use this expression to tell someone that they should act impulsively and they should think before they act. We can also use it condescendingly to tell someone that they made a poor decision. 'You weren't using your head' or 'next time, use your head'

= think! in Chinese 'dong dong naozi' move move your brain. stir your brain,

Tom: Joe insulted me, so I am going to beat him up (hit him) tomorrow. Mona: USE YOUR HEAD, dude! If you hurt him, you will get into big trouble with the law. Then you will not be able to get that good job that you want. Tom: You're right! I guess that I would be hurting myself if I hit Joe. Mona: Just ignore Joe. Everybody knows that he's a jerk (someone who does or says stupid things).

It means to think about something or use your brain.