Definition: A complex sentence is made up of an independent clause (the main clause) and one or more dependent clauses.
The INDEPENDENT CLAUSE has a subject and verb and can stand alone as a complete sentence. It is also called a simple sentence.
Example: John wrote an amazing paragraph.
The DEPENDENT CLAUSE also has a subject and a verb, but it cannot stand alone. There are two types of dependent clauses, those that begin with subordinating conjunctions and those that begin with relative pronouns.
Examples:
When John wrote an amazing paragraph (subordinating conjunction)
Who wrote an amazing paragraph (relative pronoun)