Oxygen is an amazing substances that also has a variety of applications in our every day lives.

Respiration:
•    Every living creature and plant requires oxygen to survive.
•    Oxygen therapy is prescribed for patients diagnosed with chronic obstructive pulmonary disease (COPD) as well as other medical conditions, that require oxygen to be administered at home to aid in the treatment of that condition. The use of pressurized oxygen therapy has also provided outstanding medical benefits.
•    Oxygen is a standard treatment for many patients that find themselves in hospital, which have a huge supply on site.
Metallurgy:
•    The production of steel is reliant upon oxygen where it is used in a blast furnace to turn carbon into carbon dioxide, which reduces the iron oxides to pure iron.
•    Oxygen is also used in torches for cutting and welding. Oxygen reacts with hydrogen in which it can heat to over 5,000 degrees. These torches can cut through or weld together most metallic substances.
Rocketry:
•    As a liquid, oxygen is used widely both medically and industrially, most commonly as an oxidizing agent for use in missiles and rockets where it reacts with liquid hydrogen to produce the thrust for take-off. Astronauts’ spacesuits have close to pure oxygen.
Chemical Synthesis:
•    Hydrocarbons are broken apart by heating them with oxygen. This method is used to induce combustion in order to produce water and carbon dioxide. Also if the mixture is controlled it can break apart the hydrocarbons to produce acetylene, propylene and ethylene.
•    Oxygen is also used at plants that treat sewage or purify water. Oxygen is pumped through water to increase the production of natural bacteria, which break down waste products.
•    Oxygen as a gas is required to produce energy in industrial processes, generators and ships and it is also used in airplanes and cars.
References: http://www.ehow.com and http://www.usesof.net/uses-of-oxygen.html