aptitude allows you to work with several “views” at once. A “view” (sometimes called a “screen”) is simply something that can appear in the area of the screen below the menu bar. The most common view is the package list, but download views are also common.

When several views are open at once, a bar listing all the active views will appear at the top of the screen. For instance, if I examine apt by pressing Enter, then examine libc6, the screen will look something like this:

[D]

You can close the current view using Views → Close (q). To switch to the next or previous view, use Views → Next (F6) and Views → Prev (F7), or click on the view's name at the top of the screen; you can also find a list of all active views in the Views menu.

As shown above, some commands (for instance, viewing information about a package) will create new views automatically; you can also explicitly create a new view using Views → New Package View or Views → New Categorical Browser.