A verb is in active voice when the subject actually performs the action. The subject is active in active voice.
Here is an example of Active Voice:
The dog buried the bone.
Dog is the subject of the sentence, and dog does the action in the sentence – he buries the bone.
This is an example of Passive Voice:
The bone was buried by the dog.
This time, bone is the subject – but bone is not doing the action. The action is happening to the bone. The bone is being buried.
Here are more examples of Active Voice. Notice that the subject is doing the action.
The girl rode her bike.
The choir sang a song.
Bob planted the seeds.
Now look at these Passive Voice sentences:
The bike was ridden by the girl.
The song was sung by the choir.
The seeds were planted by Bob.
Bike is the subject, but bike is doing nothing active. It is just being ridden.
Song is the subject, but song is doing nothing active. It is just being sung.
Seeds are the subject, but seeds are doing nothing active. They are being planted.
In active voice, the subject does the action. In passive voice, the subject is acted upon, but the subject does no action. The subject is passive.