Go to the Hostgator.com website Click Here
For everything you need to know, just watch this video tutorial - Click Here
Hostgator will send you aan email with all the details related to your account - be sure to save it in an easy to remember place for later.
They will also require you to activate your account so just phone them, tell them your domain name and that you want to activate the account. They will ask for your pin number or last 4 digits of your credit card to verify that it is your account and they will activate it immediately.