All you did was delete a shortcut for an app. You dont necessarily retrieve it, just put another shortcut on your desktop/home screen. You should be able to long press the desktop, click app, and then choose the app you want to be on there.
What was the app? Just long press on it in the app drawer and drag it where you want it. If it was a widget then long-press on the home screen where there's enough room for it and choose "Widget" from the menu that pops up.