A verb is a word which tells us what a person or a thing is doing.
- He ran fast.
- The birds flew away.
- John opened the can.
Here the verbs ran, flew and opened tell us what the nouns he, birds and John do. A verb is the most important word in a sentence.
Now read the following sentences.
- She is a good girl.
- There are fifty students in the class.
Here the verbs is and are tell us not about an action, but about a state of being or existence.
Now look at the following sentences.
- They have a house in the city.
- She has two children.
Here the verbs have and has indicate possession.
Thus we find that a verb is a word that tells us about an action, a state of being or existence, or possession.