1. Respiration: This is the most fundamental use of oxygen. All living organisms, from humans to plants, require oxygen for respiration. It's used to break down food and convert it into energy.

2. Industrial Processes: Oxygen is used in many industrial processes. For example, it's used in steelmaking to remove impurities, in welding to produce a hotter flame, and in the production of chemicals.

3. Medical Applications: Oxygen is vital in medical settings. It's used to treat patients with respiratory problems like pneumonia and asthma. It's also used in surgery and during emergencies.

4. Rocket Propulsion: Liquid oxygen is a key component in rocket fuel. It's highly reactive and, when combined with other fuels, provides the necessary thrust for space travel.