I see that a lot of games change the brightness, how do I do this? I notice they have a table to refer from in their sprite sheets, but that's all I know.

Mandatory tutorial from one of the best PICO-8 game:
https://hackernoon.com/pico-8-lighting-part-1-thin-dark-line-8ea15d21fed7

You’ll get everything and more!

There's also the very useful fade generator here : http://kometbomb.net/pico8/fadegen.html