Most versatile punctuation mark in English
Ways to use a comma:
separating a list of three or more items
setting off non-essential information
linking closely-related independent clauses with a coordinating conjunction (i.e. FANBOYS)
Lists (of Nouns, Modifiers)
Commas can be used to separate items in a list or series
Any list greater than 2 items requires commas between each item
"I love Taylor Swift, Kanye, and Beyonce" requires commas because the list has 3 items. However, "I love Kanye and Beyonce" doesn\'t use a comma because it contains only 2 things...pretty simple, right?
It\'s important to keep in mind that lists can be made of any part of speech
"I wanted his hipster glasses, cargo shorts, and skater-boy shoes" lists  nouns
"I swam, biked, and ran in our school\'s triathlon" lists  verbs
"The skunk was big, hairy, and smelly" lists  adjectives
"I behaved foolishly, beastly, and wildly at the party" lists  adverbs
Remember: the ACT will  always  use the Oxford comma...don\'t forget!
Non-Essential Information
Commas often set off clauses not essential to the meaning of a sentence
If this information appears in the beginning, it will be followed by a comma. If it\'s in the middle of the sentence, it will be surrounded by commas. It never appears at the end of a sentence
In the beginning of sentence: "In May, I will buy a hoverboard."
In the middle of sentence: "The man with the shady mustache, whom I saw walking down the street, kept winking at me."
There are seven types of clauses that can be set off this way (bear with me here)
Appositive : A noun phrase providing a specific description to a following piece of information
"Abebe, a videogamer, coded his own videogame." "A videogamer" = specific description that follows "Jason."
Relative clause : provides more information about noun it\'s describing -- contains who/whom/whose/which and a verb
"Shonda, who typically likes fried chicken, only ate french fries when she went to KFC." John doing well on tests = extra information
Participle clause : similar to a relative clause, but uses a participle to provide additional information - a participle being a verb ending in the "ing" suffix
"Andres, eating grapes, choked and died." "Eating" = participle and "eating grapes" = participle clause
Temporal clause : provides time for when something happened
"When Lady Gaga comes to town, I\'m going to dress up as an egg." The time I\'ll dress up as an egg = "when Lady Gaga comes to town" (temporal clause)
Causal clause : provides cause of action
"Because he saw a clown, he peed his pants." Seeing the clown caused him to pee his pants
Contrast clause : provides contextual information, making events of the main clause unexpected
"Although I\'m not a superstar, I\'m still divalicious." Words like "although," "however," "regardless of" = contrast
Conditional clause : states that events of the main clause are dependent on something else (the  effect  of something else happening)
"If I meet Zayn Malik, I\'m going to give him my number." "If" = the conditional state. In general, look for "if/then" sentences
TIP : Try reading the sentence without the information set off by commas. If it still makes sense afterwards, then the information was non-essential
Comma + Coordinating Conjunction
Commas connect two clauses that could be complete sentences on their own. This can ONLY be done when the two sentences are closely related
The sentences "Ani drinks coffee every day" and "She\'s addicted to caffeine" could be joined since both relate to Ani\'s relationship with coffee
However, "I never miss an episode of The Walking Dead" and "Conrad will go to Oologah, Oklahoma in October" have absolutely nothing to do with each other, so it doesn\'t make sense to combine these sentences
IMPORTANT: For a comma to connect two complete sentences, the comma  must be followed by a FANBOYS conjunction
FANBOYS stands for:
F or,  A nd,  N or,  B ut,  O r,  Y et,  S o
Example 1:
"The dj started playing her set shortly after they turned up."
"the dj" is the subject, "started" is the verb, and it represents a complete thought = independent clause
"It took them longer than usual to finish their Chipotle bowls."
"it" is the subject, "took" is the verb,