The comma is used to indicate a pause between parts of a sentence.

Uses of the comma

To mark off a noun

• James, can we bank on him?
• Mary, have your meals.
• John, come here.

After an introductory phrase or clause

• To be honest, I have little interest in politics.
• For God’s sake, leave me alone.
• In the name of justice, be fair to that poor man.

To indicate the omission of a verb in cases where repetition should be avoided

• My brother bought a watch and my sister, a camera. (= My brother bought a watch and my sister bought a camera.)

Before and after words used in apposition to a noun

• Winston Churchill, the statesman, was also an eminent writer.
  Janaki, my sister, is an eminent cardiologist.

To separate two or more nouns, adjectives, or adverbs that come together

• England, Russia and France formed an alliance.

To separate a participial phrase

• Feeling tired, I went to bed.
• Being fat, she couldn’t run fast.

Before and after words or phrases let into the body of a sentence

• She had, surprisingly, paid for everything.
• The boy had, in spite of all the hardships he faced, managed to succeed.

To separate a subordinate clause from the main clause

• After he had finished his job, he went out.
• When I opened the door, the cat jumped in.

The comma can be omitted when the subordinate clause goes after the main clause.