You invoke it with a key press that doesn't infer with other shortcut keys, like Win+Q.
It display a small window at the location you want. You type a few letters of a command shortcut. It autocompletes it. Hit Return, the application is launched.
Pro Option to pass an argument via $W$ parameter
Example: Set the filename or URL to execute to a web browser app, and enter the following in the Parameters text box: http://www.google.com/search?hl=en&q=$W$
When the magic word is executed, a "Dynamic input" dialog is displayed. The text entered in that dialog is passed to $W$.