What is an active an passive verb?

Answer 1

In a active sentence we can see who or what does the action of the verb:

The dog chased the cat. -- The dog does the action of chase.

In a passive sentence we don't have to know who or what does the action of the verb:

The cat was chased.

If you want to add who or what does the action (the agent) in a passive sentence then you use by + noun or noun phrase.

The cat was chased by the dog.

The verb form for passive sentences is be + past participle.

The sugar is kept in the cupboard.

The house is being built next year.