You can use your website builder to start designing and making changes to your website by following these steps - log into your member panel, click on My Services> Current Services> Sitebuilder Hosting> Service Control Center> Manage.
Clicking on manage button will take you to your site interface where you can start creating or editing your website as per your requirements.
Click here to get detailed procedure for building and managing your website using website builder tool.
Note: In some cases, in order to use website builder, you may need to change your name server details.
Learn how and when you need to change your name servers through the previous article: Do I need to make some changes to the name servers in order to use website builder?
Also, here's a quick guide to creating your website with the Website Builder tool : Learn how to build your website easily in minutes?