How do I even turn that thing on?

[CounterPillow]

So if I'm not mistaken, red in pin 6, blue in 10, USB in PC, power the board on, screen command, and then black in 8?
Or blue and black in reverse order?
Because either way didn't work.

Blue in pin 8, black in pin 10.

Make sure that in the screen command, the baud rate is set to 1500000. Personally, I just use picocom: picocom -b 1500000 /dev/ttyUSB0

Also make sure you're using the right serial port, a USB adapter will usually show up as /dev/ttyUSB0

Oh, also ensure the BAT ON-OFF jumper is in place. It's near the eMMC connector. Some early boards were shipped out without it, in that case you can take a jumper wire (e.g. an unused one from your uart adapter) and use it to connect across the two pins.