Inhalational anaesthetic substances are either volatile liquids or gases and are usually delivered using an anaesthesia machine.
An anaesthesia machine allows composing a mixture of oxygen, anaesthetics and ambient air, delivering it to the patient and monitoring patient and machine parameters. Liquid anaesthetics are vaporized in the machine.
For the mechanism of action see here
Many compounds have been used for inhalation anaesthesia, but only a few are still in widespread use. Desflurane, isoflurane and sevoflurane are the most widely used volatile anaesthetics today.
They are often combined with nitrous oxide. Older, less popular, volatile anesthetics, include halothane, enflurane, and methoxyflurane.
Researchers are also actively exploring the use of xenon as an anaesthetic.