`xlock` really does nothing, it only wraps [`i3lock`](https://github.com/i3/i3lock) screen locker into [systemd](https://freedesktop.org/wiki/Software/systemd/) to allow a seamless screen lock. Your screen stays the same, the mouse pointer works, but you can't do anything. You just have to type your password, press enter and here you go .
The whole wrapper interfaces through a random file at `/tmp/RANDOM.xlock`. To lock your screen, simply delete this file. After the install the service 'xlock@USER.path' with `USER` being the user that launched the install. To start it `systemctl start xlock@USER.path`, at the install it is enabled by default, thus it is launched when you boot.