What was the appearance of pyramids?

Unclear on exactly what you are asking here because I'm not sure if you didn't mean to ask "When" instead of what. Imhotep was the first builder of a pyramid for his Pharaoh Djoser/Zoser (spelling varies) ca 2630–2611 BCE. He began building what was to have been the largest mastaba, from the Word meaning bench due to there long flat rectangular single story appearance with little to no exterior decoration, which had been the previous burial chambers of the earliest Pharaohs but he just kept adding smaller mastabas on top of the first creating what we know as the Step Pyramid and the first Pyramid.