Look for the windows binaries. Place the exe in a safe place on your computer that you will never move it from. For me this is ~/Desktop/Applications/ffmpeg. Add it to your shell path with notepad $profile and then add $env:Path += ";[path to the ffmpeg binary]".
Go to your MPV install location. Make a new folder called scripts and place slicing.lua inside.
The script will automatically save videos to ~/Videos/Clips/. You can adjust this on line 8 at the top of the lua script. The bitrate also autmatically targets a 7.5mb file size. This can be adjusted line 59, where the default configuration is 60 (in megabits).
Press c at any point in the video (take care not to do capital C) and press c again anywhere else. Note that the progam will not extract the clip if it reaches the end of the video before you press c.
After marking the video for the second time a cmd prompt window should open and automatically run ffmpeg. Leave it open until it finishes on its own, depending on the length of the clip it could take a long time.