Dictionaries such as Merriam-Webster and Collins give definitions of linking verbs with examples of usage. In addition, CliffsNotes.com provides explanations of how to use linking verbs and examples.
A linking verb is one that does not express an action, but links the subject to a noun or adjective that provides a more detailed description. The verb "to be" is one of the most common examples of a linking verb, and using the words "is" or "are" in a sentence is a standard form of linking. However, some verbs can function as either linking or action verbs. For example, one can feel hot, but one can also feel for an object; "feel" is a linking verb in the first case and an action verb in the second.