The Site Builder allows an administrator to add various modules and configure options for almost every page on the site. It also allows you to control how your navigation bar is organized as well as which HTML ads appear in your header, and what the site logo is.
The AdminCP (Admin Control Panel), like the Site Builder is used to manage your site. While the Site Builder manages the outward facing appearance of your vBulletin site, the AdminCP controls the backend operations of your site. From usergroup permission settings to human verification options, the ability to modify and control these options can be found in the AdminCP.