Clauses are related word groups that contain at least one subject and one verb. Clauses can be independent or dependent.
Independent clauses can stand alone or can be joined to other clauses.
Seniors are first to pre-register. Independent clause, contraction independent clause. The girl drove to the movies, but she forgot to pick up her friend. Dependent clauses contain at least one subject and one verb, but cannot stand alone. These clauses are dependent on the main clause.