First, go to
www.MailChimp.com and sign up for an account. If your list is small, their accounts are free! After you have created your account, create at least one list and make sure you retrieve the list ID and your API key, as these will be required to configure the MailChimp module.
Next, download and install the MailChimp module. Configure the module using the appropriate API Key and list ID. It's that simple!