Many students have a difficult time making sentences with the passive and active voice and they are not sure when to use it. Here are the simple rules:

If you are active, you are doing something. In a sentence written in active voice, the subject of the sentence is doing the verb.

The lady played the piano.
The driver drove the car.

If you are passive, something is done to you. In a sentence written in passive voice, the subject of the sentence is having the action of the verb done to it by something else.

The piano was played by the lady.
The race car was driven by the driver.