To wash grapes place the grapes in a colander and run the grapes under some cold running water.
While running the grapes under cold running water you should also gently rub the grapes which can help to remove any debris or dirt.
Then you can pat the grapes gently to dry them with a clean towel such as a paper towel or air dry the grapes.
If you want to more thoroughly clean the grapes you can also soak the grapes in a bowl of cool water along with a tablespoon of baking soda or even a splash of vinegar a couple of minutes and then rinse the grapes under cold water again.
If not eating the grapes the grapes should be refrigerated to help prolong their shelf life and freshness.
Grapes will last up to 3 weeks in the refrigerator and at room temperature grapes will last only a couple of days.