Types of Conjunctions
**Coordinating Conjunctions—connect grammatically equal elements—for, and, nor, but, or, yet, so
**Correlative conjunctions—pairs of conjunctions that connect grammatically equal elements. Example: The work is not only profitable but also pleasant.
** Subordinating conjunctions—introduce subordinate clauses, usually adverb clauses.
**Conjunctive adverbs—indicate relation between independent clauses. Example: I ate breakfast; however, I am still hungry.
Coordinating Conjunctions Punctuation
**Thumb test--do you have two complete sentences on each side of the conjunction?
**When the coordinating conjunctions join two independent clauses, a comma is placed before the conjunction.
**When the coordinating conjunction joins parts of a compound subject, predicate or object, no comma is used before the conjunction.
It was after midnight, and I missed my bus. (compound sentence)
I missed my bus and forgot cab money. (compound predicate)
Subordinating Conjunction/Adverb Clause Punctuation
**Adverb clauses begin with subordinating conjunctions (common ones—if, as, because, since, after, before, although, though, unless, while, so that, in order that, that, than, until, when)
**Adverb clauses mainly emphasize verbs, answering how, when, where, why, to what extent
**When an adverb clause appears at the beginning of the sentence, a comma is placed at the end of the introductory clause.
**No commas are used when an adverb clause appears at the end of the sentence.
Punctuation--The two above sentences were actually your examples. In other words, introductory adverb clauses have commas after them; ending adverb clauses do not take a comma.