Frenos translates into brakes and are the equipment in a vehicle or bicycle that you use for slowing down or stopping. Basically, the sentence usamos los frenos para parar el coche means we use the brakes for stopping the car. So usamos is the conjugation of the verb usar for the first person plural in the simple present. Finally:
- ¿Para qué usamos los frenos?
- Usamos los frenos para parar el coche.
