Diving schools provide instruction and organised activities for people learning to dive or developing their skills. Courses may cover introductory experiences, pool-based training, open-water qualifications and further subjects such as navigation, buoyancy, rescue skills or specialist diving. Training typically combines theory, equipment familiarisation and supervised practice, with the level and conditions depending on the course and the participant's experience. Schools may issue or arrange recognised diving qualifications through training organisations. Other activities offered can include guided shore or boat dives, snorkelling sessions, underwater tours and supervised dives for qualified participants. Some businesses hire or sell equipment such as masks, fins, wetsuits, regulators and buoyancy devices, and may provide cylinder filling, equipment servicing or advice on fitting and use.