Comma ,

1. Use a comma “,”to:

 Surround expressions that interrupt the sense of the sentence
Example:
She is, as you know, very happy.
 Surround the name or title of a person directly addressed
Example:
 
Could you, Frank, figure out this problem?
Yes, Professor, I will. 
 Surround degrees or titles used with names
Example:
 
Professor Wiseman, Ph.D., is going to give some courses.
 Separate two adjectives when the conjunction "and" 
can be inserted instead
Example:
She is really a nice, educated woman. 
 Separate the day of the month from the year and after the year
Example:
On Monday, April 26, 1985.
On Monday, April 26, 1985, in Massachusetts. 
On Thursday, 1936, in Caracas.

(Omit the comma after the year if just the month and the 
year are used)
 Separate a statement from a question tag
Example:
She didn’t come, did she?
 Separate the city from the country and after
Example:
She has been living in Los Alamos,New Mexico, USA, 
since 1937.
 Separate introductory words such as well, however, now, 
or yes: before a main clause
Examples:
Yes, she did.
No, she cannot.
Yes, I do come as soon possible.
 Separate independent clauses when they are joined 
by any of these seven coordinating conjunctions: 
and, or, for, but, nor, so, yet.
Example:
She closed the window, but the bird is still whistling.
 Separate an adverb clause and the rest of the sentence
Example:
 
Before she comes, she had prepared the stuff.
 Separate an -ly adjective with other adjectives (not a hyphen) 
Example:
He was a friendly, wise man.
 Give contrast in a sentence
Example:
The idea is yours, not mine.
 Surround parenthetical expressions
Example:
 
She is, we have remarked, as fit as fiddle. 
 Separate the name of the speaker from the direct speech
Example:
 
"I didn’t see him," she said.
She said, " I didn’t see him."
 Separate a weak clause from a strong clause
Example:
 
I am very sorry, I cannot.
 Separate parallel structures in series (adjectives, nouns, 
phrases and sentences) 
Examples:
 
He saw a bird, a star, a cloud and a plane in the sky.
He was supposed to clean up the house, do the dishes, mow 
the grass and do his homework.
 Surrounded nonessential descriptions:
(Nonessential: regarding the meaning)
Example:
The woman, who had a blue hat, left the park without her dog.
 Separate big, introductory prepositional phrases
Example:
Before the First calculator in 1642, I was difficult to do some 
calculations.
 Separate introductory clauses whish use common starter 
words: After, although, as, because, if, since, when, while. 
Examples:
Because his car was broken down, he stayed at home.
While he was sleeping, she knocked at the door.
 Separate introductory phrases that come before the main clause
(Introductory phrases: with three or more words)
Examples:
To be nice, you should tell the true 
Keeping in mind all the words, she went to introduce 
herself to the group.
 Surround a contrast in the sentence 
Example:
 
She asked him, not boldly, the question whish he 
never wanted to hear.
 To prevent possible confusion or misreading wherever 
necessary
Example:
To him, everything is all right. 


2. Don't use a comma:

 If the subject does not appear in front of the second verb
Example:
He came yesterday and was not aware of the hurricane.
 To separate the subject from the verb
Example:
Her mother (,) was sixty-seven years old last month.
 Between the two nouns, noun phrases, or noun clauses in a 
compound object or compound subject
Examples:
The book I read, and the Frank’s were the same (compound subject)
She have seen her friend, and her sister didn’t care about.
 After the main clause when and before a dependent 
(subordinate) clause 
Example:
He was late, because his car was broken down.
 Between two verbs or verb phrases in a sentence
Example:
He bought a car last week, and lost its keys in a gas station.