This simplistic package is meant to be used as a way to close whatever window is active by clicking it on the panel, and keep clicking until the Desktop is active, and then click again causing your Desktop to close thereby logging you out.
To use it as intended, after installation, you should add it to a launcher. For example, in Xfce, you could
- right-click on a panel and choose 'Panel -> Add New Items'
- click 'Launcher', then 'Add'
- click 'Close'
- right-click the question-mark now showing on the panel, and choose 'Properties'
- click '+'
- type 'close' into the search box
- choose 'Close Active'
- click 'Close'
Now, instead of a question mark, you will see a big 'X'. When clicked, it will do what's described in the first sentence above.