WHAT IS A LINKING VERB?

These verbs link the subject to the subject complement. While the most common linking verb is "to be", other verbs can work as linking verbs (also known as copular verbs).
In order to check if a verb is a linking verb, merely substitute it with the verb "to be". If the sentence reads well, with no drastic change in the sense, the original verb is working as a linking verb.
In essence, the linking verb creates a "kind of descriptive tendency" for the subject complement. That is, the subject complement is "almost describing" the subject.

e.g. AFRICA IS A LARGE CONTINENT. (BE - linking verb)
- "Africa" (subject) is linked to "a large continent" (subject complement).
- "a large continent" describes "Africa"

e.g. BACKPACKING HAS BECOME LESS POPULAR. (BECOME - linking verb)
- "Backpacking is less popular" – "become" can be substituted with the verb "to be".
- "Backpacking" (subject) is linked to "less popular" (subject complement), which describes "Backpacking".

Other linking verbs, or copular verbs, are: to appear, to seem, to look (like), to sound (like), to feel, to taste (in the sense of having the taste of), to smell (in the sense of having the smell of) etc.

e.g. GODFREY SEEMS A LITTLE WORN OUT AFTER THE GAME. (SEEM - linking verb)
- "Godfrey is a little worn out" – "seem" can be substituted with the verb "to be".
- "Godfrey" (subject) is linked to "a little worn out" (subject complement), which describes "Godfrey".

NB: Linking verbs are not always followed by a subject complement. They can link the subject to an adverb.

e.g. THE BROKER WAS OUT. (BE - linking verb)
- "out" is an adverb. Adverbs cannot be subject complements.
- The subject is linked to an adverb by a linking verb. In this case, the linking verb acts in an "intransitive" manner. I am not saying that linking verbs are "intransitive", just that, when they link subjects to adverbs, it feels a little "intransitive".