An appositive refers to a word (noun or pronoun) or a phrase that usually goes with another noun or pronoun to identify or explain it. For example, my brother, the chief security officer of my company, celebrates his birthday tomorrow. In the example above, "the chief security officer of my company" is the appositive in that sentence.
The appositive is trying to add more information to the word "brother" so that the listener can have a better understanding of the person under discussion. Another example: John, a 42-year-old father of four, was founded dead in his house. The second example also follows the explanation given to the first one, meaning "a 42-year-old father of four," which is the appositive phrase. In the two examples given above, the two appositives used came after the nouns they explained.
However, appositives can also come before the words they are trying to identify or explain. For example, A powerful minister of God, Thompson John, is known for different miracles and wonders. The appositive here is " A powerful minister of God."