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 French conjunctive phrases end in que and all are subordinating conjunctions.
Connectives are links: they combine words, phrases, or sentences. Connectives do not constitute a single part of speech, but rather a category of terms including all conjunctions and prepositions as well as certain types of adverbs and pronouns used in this way.
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.
Some coordinating conjunctions are used in pairs or multiples to emphasize the connection between two or more grammatically equivalent words or phrases. These emphatic coordinating conjunctions, aka correlative conjunctions, might connect adjectives, nouns, adverbs, verbs, or even independent clauses.
French has two closely related negative conjunctions: ni (nor) and ne ... ni ... ni (neither ... nor).
Many French conjunctions and conjunctive phrases require the subjunctive, notably those which link cause and effect.
Subordinating conjunctions connect two unequal clauses: a main clause and a dependent or subordinate clause.
There's a way to use the subordinating conjunction que that isn't often taught in school: as a substitute for another conjunction. This usage is neither informal nor unusual, but it is limited to a specific construction and for a specific reason.