What does common linking verbs are forms of the verb be mean?

The forms of be are: am / is / are / was / were / been

They are usually/commonly used as linking verbs. They link the subject with a complement.

subject = I - I am hungry.

subject = is - My sister is ten.

subject = we - We are from New Zealand

subject = I - I was a doctor.

subject = The boys - The boys were late.

subject = Jack - Jack has been a good brother.