Sixth Dans and above may wear black belts if they wish and generally do so except for formal demonstrations. The top international competition men are usually 4th Dan and they acquire higher grades as they grow older through knowledge and service to the sport. The club you join should have a proper judo mat and will provide a judo kit. If these are not available some surface soft enough to absorb a heavy throw is necessary with some loose strong clothing tough enough to take a lot of pulling. You will then be ready for your first lessons in Judo.