circles are moslty used for friendly characters

triangles are pointy and sharp they are mostly used for evil characters

squares are strong firm and boring.

this is bob from a circle world i made him using the circle tool and coloring them in after i made him i moved onto the backround and the other characters

this is triangle from a cliff somewhere, triangle was made using the triangle shape tool that was placed together to create a shape that can look like a character

this is Steve from a flat world, Steve was made from the square tool which i recolored to give the illusion of shape around the head and in the eyes.