What is the difference between coordinating conjunction, subordinating conjunction and correlative conjunction ?

A conjunction that joins two independent clauses is called a coordinating conjunction. The two clauses that are joined by the conjunction are of equal rank and do not depend upon each other. For example:

Days are hot and nights are cool.

She is poor but she is sweet.

A conjunction that joins two clauses one of which is dependent upon the another is known as subordinating conjunction. For example:

He flunked because he did not study.

I will come if you want me to.

Conjunctions that are used in pairs are called correlative conjunctions. For example:

Either my sister or I will buy a gift for my mom.

Not only did I wrote a letter to you, but also I called you up.

(In the sentences above, either-or and not only-but also are correlative conjunctions.)