A linking verb "links" a subject with a noun ("predicate nominative") or an adjective ("predicate adjective"). Linking verbs
This story may help you remember the major linking verbs:

Stanley Grabs was a young boy with a problem: he simply could not remember his linking verbs. He asked his teacher, Mrs. Bee, for help.  

Stanley Grabs: “Hello, Mrs. Bee. I hope you can help me with a problem I am having. I can’t remember my linking verbs.”

Mrs. Bee: “Oh, Stanley, remembering the linking verbs is easy! I can help you!”

Stanley Grabs: “You can? That’s great!”

Mrs. Bee: “Well, Stanley, all you have to do is remember that there are three main groups of linking verbs. The first group consists of all the forms of to be. Do you remember these?”

Stanley Grabs: “I do! They are…

  • am
  • is
  • are
  • was
  • were
  • be
  • being
  • been…

 Mrs. Bee: “Right! Good going, Stanley. The next group of linking verbs contains the sense verbs. You need to be careful with these because some of the senses have two associated verbs. One way to figure out whether a sense verb is action or linking is to say ‘good’ after it. Action verbs can’t be followed by ‘good’ because it is an adjective, and only adverbs can modify verbs. Let’s go through them together.”