Here's why:
* Conjunctions connect words, phrases, or clauses.
* Subordinating conjunctions introduce dependent clauses (clauses that cannot stand alone as a sentence).
Example:
* "When the bell rings, we will go to lunch."
In this sentence, "when the bell rings" is a dependent clause introduced by the subordinating conjunction "when." "Will go to lunch" is the independent clause.
Let me know if you have any other grammar questions!