Here are some rules about using commas. In a date, the comma goes after the day (number).

Example: The twins were born on April 6, 2010.

In place, the comma goes between the name of a city and a state/country.

Example: The Palace of Winds is in Rajasthan, India.

When there are three or more items in a list, each item is separated with a comma.

Example: Dolly wanted a train, a tiara, and a treasure box for her birthday.

A comma is also used in the greeting and closing of a letter.

Examples in greetings:

Dear Ms. Thimble,

Dear Uncle Heath,

Examples in closings:

Love,

Thank you,