Moodle's front page changes after a user has logged in. The content and layout of the page before and after login can be customized. Look at the following screenshot. It is the same site that the preceding screenshot was taken from but before a user had logged in:
In this particular example, the Login block is shown on the left-hand side and the Course categories and Courses as well as a course search box are displayed in the center, as opposed to the list of available courses. Additionally, the Administration block is not displayed.
Bear in mind that some implementations may not have an unauthenticated view. This is the case if a single sign-on mechanism has been implemented.