An action verb expresses something that someone or something can do. It may be a physical action such as run, bark, or roll or it may express some other sort of 'doing' such as think or change.

In the examples below, the action verbs are underlined.

The dogs barked incessantly all night long!
Many large stones suddenly rolled down the hill.
The kids thought the story was over, but it wasn't.
The colors of the leaves should be changing soon.