What it is? It colors your (or someone else's)
lineart for you. You can also use the color thing it has to guide the whole coloring more toward what you want (just a small line or even a dot of color will do)
, but you don't have to. Of course it's not perfect by any means, but it is pretty cool either way and does give some very neat results, and some ideas.
If you don't have your own lineart ready to use (to try it out)
, you can always use google and search for some coloring pictures for example.