Go to Filter - Artistic - Cutout... (8,4,2, you can use whatever setting you want but these are most common, just play around with it until you find something you like)... i think thats what you're talking about, you cant turn an image of a real person into a cartoon any other way unless you draw it, that i know of.
you cant use brushes dumbass, brushes are for bg's, using a brush will cover the image!

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