Verb

A verb shows an action or state, what something does or what something is.

Most English verbs have four parts:
1. finite forms, which change for different times or different people (e.g., am, is, are, was, were);
2. infinitive forms, which do not change for different times or different people (e.g., be);
3. -ing forms, which always end in “-ing” (e.g., being);
4. -en/ed/t forms, which end in “-en/ed/t” (e/g/, been).

Different verb types need to be followed by different things. Some verbs are followed by a noun object. These are called “transitive verbs” (from Latin trans, “across”, +it, “go”, i.e. the verb “goes across”, like a bridge, from the subject to the object).
I heard a noise.
She saw him.

Some verbs are followed by an adjective. These are called “complement verbs”, because the adjective is not an object and so is called a “complement”.
That smells good.
I feel happy.

Some verbs do not need anything after them.
We slept.
The accident happened.

The grammatical difference between verbs like see and look, or hear and listen, is that one needs a noun object and the other cannot have a noun object, but we can add a prepositional phrase to both of them.
He looked through the window. He saw me through the window.
She heard voices. She listened to the words.

We use different verb forms for different times.