Flip the switch to make the lights blink. Plug in your guitar to engage the Nine Volt Nirvana Tape Measure audio circuit (schematic).
It gives you a pretty decent boost, around 25dB, and a bit of gritty overdrive. When cranked it has a bit of a lo-fi vibe to it.
I'll try to make a video demo before too long (unless you do! Please do and I will happily post it), but my recording setup is pretty bad.
There's really only one non-obvious thing to be aware of: when your guitar cable is plugged in, the pedal is using power. Unplug it when you're not playing. This has two circuits: the lights controlled by the switch, and the audio controlled by the input cable.
NOTE: If you experience a ticking noise while playing, turn off the pedal's blinking lights. Or embrace it and shrug it off because your guitar is plugged into a freaking Christmas Tree, hanging on a bigger Christmas Tree.
You can also email me directly but you'll get a quicker response through those groups.
There are dozens of other DIY pedal communities as well, so of course you can seek help anywhere else.