Please use the helpfile before resorting to asking questions on the forum.
Your questions can and will be answered by typing /help hash tables
Particularly of interest to you will be:
I suggest you read the entire helpfile a few times before asking another question. It's no good to be spoonfed all the answers, you need to learn to look things up and figure things out on yourself. If you still have a question then, people here will be glad to help you.