This document discusses clauses and how they are used to form complete sentences. It defines a main clause as containing a subject and verb and expressing a complete thought on its own. A subordinate clause does not express a complete thought on its own and is introduced by a subordinate conjunction. When attaching a subordinate clause to a main clause, a comma is used if the subordinate clause comes before the main clause, while no punctuation is needed if the subordinate clause follows the main clause.