Traditional Zentangles are created on 3.5" (9x9cm) squares, done with black ink on white paper, and can have areas of grey shading, but there is nothing to stop you haveing them any size or shape you like, or adding colo0ur.
Drawings are created using simple shapes: lines, dots, circles, curls, swirls, squiggles. It doesn't matter which way up the image goes when it's finished.
Zentangles are organic, and the idea is to see what happens. Just keep drawing so that the shapes morph into something new.