Finite forms

Every English verb has “finite forms”. These are the forms which change for different people or different times.
I like coffee.
She likes coffee.
He liked coffee when he was young.
We only use like for the past, not for the past, and only with I or you or we or they, or with a plural noun subject. We only use likes for the present, not for the past, and only with the pronoun subjects she or he or it, or with a singular noun subject. We only use liked for the past (e.g., when he was young), not for the present.

When a verb has more than one word, the first word is always a finite verb.
The window was broken.
He is sleeping.
They are going to win.
In each of these sentences, we must change the verb if we change the subject from singular to plural, or from (third person) to (first person) or (second person), or if we change the time.
The windows were broken.
They are sleeping.
They were going to win.
The other words in the verbs do not change because they are not finite.