either because you have multiple faces on there (which probably isn't the case for you)
most likely its because your faces aren't planer (flat along one axis)
solve this by drawing more edges
faces should be kept to 4 or 3 sided polygons where possible
that's a "Ch" pronounced as a "K"
Computer skills I should have:
Maya, XSI, Photoshop, AfterEffects, Motion, Illustrator, Flash, Swift3D