linking verbs don't express action. Instead, they link or connect the subject to more information about the subject. 'Is' often serves as a bridge between the subject and a description or identification of that subject.
'Is' is used with singular third-person subjects, such as 'he,' 'she,' 'it,' or singular nouns like 'the dog' or 'the book.' 'Is' is not typically used with plural subjects. Instead, 'are' is used. 'Is' also acts as an auxiliary verb when forming the present continuous tense. In this role, it helps indicate an ongoing action.
He is a doctor.
The book is interesting.
She is running.
It is raining.