accidentally removed my taskbar. how do I reactivate it to be displayed again.

I just need to re-activate the task bar as it was after I installed the kubuntu

Right click onto your workspace (desktop). There you can add a new panel. Make sure your workspace is unlocked (same menu). At this point you have a clear panel without anything. Now you need to add all the plasmoids doing the work in your panel (taskbar). A menu, desktop switcher, maybe a clock, the part where open windows are shown and the part with the notifications and the icons. (don't know the english titles, sorry). There are different ways to do that, but the right-click menu of the workspace offers this option too (add widget). Then simply drag'n'drop them on your newly created panel.

Here's a link showing all the important stuff about plasma in a series of screencasts: http://userbase.kde.org/Plasma/FAQ/HowTo
Everything I wrote is shown there too. Take a look if you're unsure.