

The items in the menu are:
Search the installed package list for a package, the name of which contains the entered string
Produces a list of packages that contain the entered file name, selecting a line will display the information on that package. It behaves slightly differently for RPM (where you have to enter the exact file name) and DEB (where you can enter a regular expression).
Searching for uninstall files uses the apt-file command, this updates the database that apt-file uses.