The list of packages is the primary interface to aptitude. When aptitude starts, the list is organized into a number of groups, as can be seen in the following screen shot:
Empty groups of packages are automatically hidden by aptitude, so you may see more or less groups than appear in this screen shot.
In the screen shot above, the first group (“Installed Packages”) is highlighted to indicate that it is currently selected. You can move the selection up and down with the arrow keys; note that the description below the package list changes as you do so. To “expand” a group, press Enter while the group is selected:
As you can see, the “Installed Packages” group has been expanded to reveal its contents: it contains a number of subgroups, loosely defined by what types of software they contain. Expanding the “admin” section by selecting it and pressing Enter, we see:
The “admin” group contains a single subgroup, the “main” Debian archive. Expanding this group reveals some packages!
To save time, you can use the [ key to expand all the subgroups of a group at once. Selecting “Installed Packages” and pressing [ would have immediately revealed the packages in the screenshot below.
In addition to the arrow keys, you can move the selection through the package list a page of information at a time using the Page Up and Page Down keys.
When there is more information in the lower half of the display than fits into the available space, the a and z keys can be used to scroll through it.