Linux and KDE Tutorial?

Hi Folks, One of my PM's wanted an account on a server he's paying me to manage, so I set it up with xrdp so he can connect from his Windows desktop.   I configured it to run Plasma and KDE. Now he's asking for a tutorial on KDE, and probably Linux in general.  Does anyone have any recommendations for a newbee to Linux?  He's heavily steeped in the Way of Windows, I'm afraid.  But at least he wants to learn. Thanks in advance, Lew