Oh! The tool helps you draw inside the colored parts!

yeah, it only colors what other things are on that layer

Yes, it writes inside your drawings. It's good for shading and opacity.

lol idk either - Akie

Yyehhhh!

I do, lol, but it's kinda hard to know what the name is- and describe it, but I'll go for the first comment

i think its called marker tool or smth its basically like what the others said, for ex, under the line art in another layer u colour in one colour(lets go with grey) after that u use this tool to just colour more specifically with other colours(whatever colours ur oc is)