Invoke Quicksilver using the shortcut you defined. From the window that appears, you can search for items in your Catalog to build commands.
To search, type part of an item's name. Quicksilver will match any part of the name, as well as abbreviations. Quicksilver will display a drop down list if there are multiple matches. Select the desired item from this list, and Quicksilver will learn the abbreviation.
Quicksilver automatically chooses an action to perform on your selected item. To view alternative actions, press the tab key to highlight the action search field, then the down arrow.
Press the return key to execute the selected item and action.