What is the meaning of comma?

A comma helps separate things.

1. items in lists. For example: I bought milk, cheese, rice, fish and bread at the store.

2. or ideas like: I am cold, and I could use some hot chocolate.

3. It helps separate a phrase from the rest of the sentence. Like: This morning, I ... or When I get home, I will... or Until yesterday, I didn't know... or At the bookstore, I bought...