How do they manifest? and form? why?
Typically sinkholes form in areas where the ground is mostly made up of carbonate rock (dolomite, calcite). Then a source of water (from a subterranean river/creek, broken pipe, or even rain water making its way down through the ground) will gradually erode the ground away. This can happen through a chemical reaction where the rocks/minerals are dissolved and carried away, or just by erosional removal of material. Once enough material has been removed, the overhead weight exceeds the support strength, and can collapse. Sinkholes can vary greatly in size, depth, and diameter.
