When KPackage is started normally (that is it has not been invoked via drag and drop and has not been given any parameters) it displays two panels with the package tree on the left, this tree shows installed packages and optionally new and updated packages as well.
The tabs on the panel select whether to display installed packages, updated packages, available packages or all packages
The package tree shows the package name, package size, the version and (in the case of an available package which would update an installed package) the version of the already installed package.
Selecting a package from the tree displays information about it in the right panel and allows:
Displaying the status information on the package
Seeing which files are included in an installed package, selecting a file from the list will open it using the file manager
Verifying files in a package, files that exist are marked with a tick, files that don't with a cross.
Uninstalling an installed package
Installing an available package
A single package is selected by clicking on the name. Clicking on the dot in the Mark column marks the package with a tick, a second click unmarks it, while Shift+left click can be used to select a range of packages.