Since linking verbs, also referred to as copulas or copular verbs, don't function in the same way as typical verbs in showing action, it can sometimes be tricky to recognize them. These types of verbs:
Show a relationship between the subject and the sentence complement, the part of the sentence following the verb
Connect or link the subject with more information - words that further identify or describe the subject
Identify a relationship or existing condition
These types of verbs are sometimes described as performing the function of an equal sign because they provide the connection between a subject and a certain state.