Before you even install KVM on your freshly installed Debian machine, you need to make sure that your machine can even run the KVM virtualization. Most computers will have to enable virtualization through the BIOS as it is mostly disabled by default.
And you will get an error when you try and install KVM. There are even some computers that can not run it all together.
The most common way to enable virtualization is by pressing either F8 or F12 as your machine starts up, to enter the BIOS. Look for System Configuration and Enable Virtualization Software.
Keep in mind that this is different from machine to machine and could be something entirely different, and the steps might be a bit more convoluted, so you might have to do a little search on the internet to work out how to do exactly it on your computer.
When that is done save and reboot the pc, and let it load up your Debian. Go to the top left corner click on Applications -> Accessories -> Root Terminal and type the password for the Root user.
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