KDE is a window manager for the X Window system. It comes with a toolbar at the bottom of the screen and
default buttons. You can drag icons from your desktop to the toolbar.
The problem is that there is no option to add icons.The trick is to drag a file on the toolbar and then edit it. Open KFM and drag the program you want on the toolbar. You can then edit it and change the settings of the new icon in the toolbar:
"Windows Linux Tips: KDE drag and drop icons"
Reference : techpraveen.com