A complex sentence is made up of one independent clause and at least one dependent clause. The dependent clause cannot stand alone as a complete thought but adds additional information to the main idea expressed in the independent clause.
A dependent clause is also known as a subordinate clause because it relies on an independent clause to form a complete thought.
Subordinating Conjunctions: These are words like "although," "because," and "while" that introduce dependent clauses in complex sentences.
The main idea refers to the central point or focus expressed in the independent clause of a complex sentence.