It is spelled as "turban" and yeah you do wear one if you are bald. The point is to keep the body in the state in which it was created and to give a distinct identity so that a Sikh can be identified in a crowd. Exceptions - medical reasons, maybe? Depends on the interpretation of the Sikh, old timers would decline medical attention and prefer to die than have to cut their hair. Most modern Sikhs would ask for forgiveness and get baptized again after getting medical help.
Some do, depends on the Gurdwara where you get baptized but 99.99% don't. They dress like women from other religions but don't cut their hair.