evdev is the open source input driver for many input devices like keyboards, mice, joysticks and more.
You need USB support, if you have an USB input device. Also you need to activate the following kernel options:
Portage uses the variable INPUT_DEVICES for enabling support for various input devices in packages. Setting INPUT_DEVICES to evdev will pull in the correct driver:
After setting this you want to update your system so the changes take effect:
To set the default layout copy the file 10-evdev.conf to /etc/X11/xorg.conf.d and edit the keyboard section, e.g. for a german layout: