Transitive verbs are those which exert an action upon the object.
I caught the ball. They asked her. He loves her.
Intransitive verbs, on the other hand, describe actions (or states) that cannot be performed on an object.
I sprinted. She summersauted. He nodded. I awoke.
Identifying Transitive and Intransitive Verbs
Try using the verb in the imperative form (information on this can be found here). You will find that transitive verbs imply an object, and it feels as though the sentence is incomplete without one…
Eat. Give. Throw.
Conversely, you will find that intransitive verbs in the imperative form function well, and the resulting sentence seems complete…
Whistle. Dance. Think.
However, some verbs can be both transitive and intransitive…
I sang vs I sang a song. I ate vs I ate some food. I polished vs I polished the cabinet with him.