This 3D animation from The Human Atlas explains how inhalers work.

Some people have difficulty breathing due to illnesses which constrict their airways. Medications for these respiratory symptoms can be given by inhalation. Common types of inhalers are: Metered Dose Inhalers (MDI), Small Volume Nebulizer, Dry Powder Inhalers (DPI).

A Metered-Dose Inhaler contains medication in a pressurized canister. To use the inhaler, take a deep breath as you push down on the canister, breathing in slowly for about 5 seconds. Hold for 10 seconds, before slowly releasing the breath. This sequence is referred to as a "puff". The doctor will prescribe your dosage for each use.

A Small Volume Nebulizer involves placing a measured amount of medicine into a chamber. A small air compressor blows a fine mist of medicine through a mouthpiece into your lungs as you breathe normally. The nebulizer treatments last about 10 minutes.

A Dry Powder Inhaler contains medicine in the form of tiny granules. DPI inhalers use a variety of methods in which to release doses of medication. With all of these methods, the patient first exhales, then, quickly inhales the powder medication through the mouth as it's released. This medication is activated by breathing.