Android 4.4 comes with an app button in the bottom panel. If it gets deleted, how do I get it back?
If you are running the Google Now Launcher this is supposedly not deletable. Other launchers allow customization and offer the button as a shortcut to a "launcher action". If you long press on an empty region on your home screen it should ask you whether you want to place a launcher action there. If you just go thru the options in that list it should be quite easy to find.
Here's are some screenshots for Nova Launcher on my i9100 running 4.4.2.