Conjunctions are

Rhetors use conjunctions to aid coherence–especially to join co-equal ideas via coordinating conjunctions and to show relationships across ideas via Subordinating Conjunctions.

Coordinating Conjunctions

Rhetors use coordinating conjunctions to join to two independent clauses–i.e., two sentences.

Subordinating Conjunctions

A subordinating conjunction connects an independent clause to a dependent (subordinate) clause.

Rhetors use Subordinating Conjunctions to show relationships between ideas.