There are two types of clauses: independent and dependent.

An independent clause expresses a complete thought and, as any clause, has one subject-verb combination and often a verb completer.

• One independent clause makes a simple sentence.
• Two or more independent clauses make a compound sentence.

A dependent clause serves to complement an independent clause and cannot stand as a sentence, even though it has a subject, a verb, and a verb completer. 

• One dependent clause in a sentence is called a sentence fragment because it does not make a complete though. e.g. Because it was fast and easy to do.
• A combination of one independent and at least one dependent clause makes a complex sentence.
• There are three types of dependent clauses: adverbial, noun, and adjective.
• A dependent clause always begins with a subordinator (explicit or implied), such as who, that, if, because, etc.