Do a net search for 'wondy quilt blocks' and you'll get a lot of info.
Otherwise ... you just cut off triangles on each side of your square ... the same on all sides ... and it will then be wonky. You can measure ___ inches from one corner and ____ inches fromt he other corner. However you do it ... it will work.
You can also look at some Escher drawings and see how they are designed. They basically were squares but the whatever was removed on one side was put on the other side.
ali