One of the eight parts of speech, conjunctions are used as connectors between grammatically related words or phrases. There are two kinds of conjunctions, depending on whether that relationship is equal or unequal.
Two or more words often join to create a conjunctive phrase, which just means a series of words that acts like a conjunction. Most conjunctive phrases end in que and all are subordinating conjunctions.
Coordinating conjunctions are small words that connect two or more grammatically equivalent words or phrases. The connected words might be adjectives, nouns, adverbs, verbs, or even independent clauses; the important thing is that they're equal and each one serves the same function in the sentence.
Subordinating conjunctions connect two unequal clauses: a main clause and a dependent or subordinate clause.