Comma

A comma has a lot of uses in grammar.

 Uses

Commas are used to separate items in a series. For example, insects, birds, reptiles, and fish belong to the animal kingdom. They are also used to separate independent clauses in series.

• Before genetic engineering, roses are red, violets are blue, but not anymore. They are also used to separate elements in a series of three or more words, e.g.,  I stand straight, closed my eyes, took a deep breath, spread my arms, and jump off the building.

Commas are used to separate coordinating conjunctions (FANBOYS)  to connect two independent clauses.
               

•  Leila enrolled in hospitality management,  but she dropped out of school after her father died.

They are used to set off parenthetical and introductory elements in a sentence. Parenthetical elements are words or phrase that can be removed without changing the thought of the sentence. They are additional information that tell something about the subject.

•  Jay is so handsome, sometimes too hot if he is shirtless, that all the lass in our village had a crush on him. The phrase "sometimes too hot if he is shirtless" can be removed in the sentence without changing the meaning of the sentence.

Adverbial or conditional clauses used in the beginning of the sentence is set off with a comma.

•  Although the tides are high, they went to the beach. 

 But when a adverbial clause is used towards the end of the sentence, the reader is left to determine whether that clause is essential to the meaning of the sentence. 

Commas are used to separate name the of the city and country, affiliation,  long numbers, as well as with dates.

•      Texas, USA

                   January 1, 2013

Commas are used to separate coordinate adjectives. They are used instead of but or and.

•       This tall, dark and handsome man is my brother.

                    The ugly, little duckling was looking for her mother duck.

They are used to set off quoted text as in dialogue.

•         "What I am saying is," my mother interrupted, "You can go to school and get a good-paying job, or you can marry at a young age and end up with a terrible husband."

   

Used to set off phrases that are contrasting.

•          I love you, not him.

                   

Never use only one comma between the subject and verb.