You can customize your desktop to great extent by adding, removing and/or moving around widgets. In Plasma - the KDE desktop - everything is a widget (also sometimes referred to as plasmoid) and therefore gives you great powers to alter things according to your liking. In order to add a widget to your panel or desktop, just click the cashew icon and select Add widgets.... If you had your desktop configuration locked, select Unlock Widgets first to be able to gain access to the widgets library.

From the library that shows up, you can now drag any widget around.