A verb can either be active or passive. When the verb is active then the subject of the sentence actually does something.
Maria hit the ball out of the park.
Michaela sang a song.
To make a verb passive you just add some form of ‘to be’ to the verb.
The dog was walked
The dog is walked
The dog will be walked
This lesson is very important to me. Time and time again, while editing, I have seen and noticed how authors are confused about using active verbs. The question you should be asking yourself is this: Would you rather read about someone who sits around and just lets things happen to them, or would you rather read about someone who actually does something?
Don’t shift. Keep your verbs and voice consistent. For examples:
When Alice pulled the fire alarm, a loud ringing was heard.
‘Was heard’ is passive here and pulled ‘pulled’ is active. This does not match!
When Alice pulled the fire alarm, the students heard a loud ringing.
‘Heard’ is active here and so is ‘Pulled’. Therefore, they match!