Sentence fragments are incomplete sentences. All grammatically correct sentences require three elements. If one element is missing, the sentence is a fragment.
The three necessary elements of a complete sentence are:
Subjects and Predicates
The subject of a sentence is the noun or pronoun that the sentence is about. It usually appears before the verb, and tells who or what is doing the action. The predicate of the sentence is usually made up of a verb and sometimes other words as well. The verb is the word that tells what the subject is or does. The verb tells whether the action in the sentence occurs in the present, past, or future.
If the sentence is missing a subject or a verb, it is a fragment.
fragment A story with deep thoughts and emotions. (No verb)
fragment Toys of all kinds thrown everywhere. (No verb)
fragment With lots of charm and charisma. (No subject or verb)
fragment Such as beets and raw carrots. (No subject or verb)
This is where many people have trouble; they think that if they can find a noun and a verb, it must be a sentence--but this is not always true. A sentence must also express a complete thought.
fragment When we go to the game.
fragment If we aren’t doing anything later.
fragment The girl who played point guard.
Each of these fragments has a subject and a verb, but does not express a complete thought. We need more information to finish each.
Complete sentence When we go to the game, we will meet up with friends.
Complete sentence If we aren’t doing anything later, we might go out.
Complete sentence The girl who played point guard scored 14 points.
Complete sentence There are only a few foods I can’t stand, such as beets and raw carrots.
Almost all fragment mistakes occur when pieces of sentences get disconnected, and they can be corrected by connecting the fragment to some information already given. When you proofread your work, be on the lookout for periods, and then scrutinize each sentence to make sure it not only has a noun and a verb, but also expresses a complete thought. Good luck!