Open up YaST2 and search for 'kernel-source'.
X-windows is the XOrg server. Previously suse used XFree86's x-windows server, but because they added requirements about including the authors names in the packaging, they switched to the XOrg offshoot.
Take a look at the description given on this rpm find page:
Perhaps your question was more general. How does X-windows defer from what you've been using? It was designed in an environment where many terminals may be hooked up to a mainframe computer. The programs run on the mainframe server, and the display is shown on the terminal. So it's designed from the ground up to work over a network. In other words, the program running may be on a different machine from where the person is using the keyboard/mouse and screen. So the running program makes requests of the machine with the display what to display.
So the X-windows terminal is for the graphics system the server, and the running program is the client.
If you are at your laptop computer, and it is networked to the desktop, you can start a secure shell session. You will get a console screen where you can enter commands. If you enter a kde or gnome program, the program will run on your desktop computer but be displayed on your laptop. So you can run a number crunching intensive program like blender from your laptop and not have to wait forever for it to generate a frame.
It's also possible to start a program without using the ssh shell, or to be at your desktop and start a program but have it display on your laptop.
blender -display laptophostname:0.0
will run the blender program and display it on the laptop.
However, there can be security concerns, so Linux uses an xauth program which has to be set up before you can do this.
You can also open up a separate display on the computer you are at now.
xinit -- :0.0 will start a new session on VT8. You can have a KDE session on VT7 and a GNOME session on VT8 for example.
About the <host>:0.0 notation. <computer hostname>:display:screen
The screen part is if you have a multihead system. So from the desktop, you can display a program on the 2nd desktop monitor. Or from the Desktop, display pictures out of the laptops tv out connector, displaying a slide show of artwork on the television, while you are answering emails!