You go to http://your.pc.ip:3000 with your phone's browser. You get some keys on the screen. You touch the keys and it plays some other keys on the pc. What worked for me were volume up, down and mute, Alt-Tab. There were other less interesting combinations like CTRL-numbers but the shortcuts can be configured in a json file. It eventually core dumped and I had to close every terminal before being able to type again (Ubuntu 16.04).