A linking verb is a verb that connects the subject of a sentence to a noun or adjective that renames or describes the subject. Linking verbs do not show action, but instead they link the subject to more information about the subject.
To identify a linking verb in a sentence, replace the verb with "is" or "are". If the sentence still makes sense, then the verb is a linking verb.
For example:
"She feels tired." (She is tired.)