In general, it is not necessary to put a comma before the word "and." However, there are situations where using a comma before "and" can clarify the meaning of a sentence or make it easier to read.

For example, you might use a comma before "and" when you have a list of three or more items. This is called the Oxford comma, and it is used to avoid confusion between the final item and the conjunction "and." Here's an example:

"I bought apples, oranges, and bananas."

In this sentence, the Oxford comma (the comma after "oranges") makes it clear that "bananas" is a separate item in the list, rather than a combination of "oranges and bananas."

In other cases, using a comma before "and" can help to indicate a pause or a change in thought. However, it's important to use commas judiciously and not overuse them, as this can make your writing harder to read.