Once your broadband service goes live you will see the broadband service on the homepage of your portal, click on this to go to your service page.
Once on your service page at the bottom of the left hand menu you will see the option "Free Hosting Account". Clicking the link will bring you to a page asking you to enter the hostname. This can be anything you want, but has to be a unique value so if the hostname entered is already in use then you will need to select a different one. The hostname will be the domain for your hosting account, although you can later use your own domain once the account is set up.
Once you have done this you will see the service on your portal homage, clicking this will bring you to the hosting account's control panel.