The document discusses three basic essentials for life: oxygen, water, and food. It then focuses on oxygen, defining it as an element, gas, and drug. It describes oxygen therapy as administering oxygen at concentrations greater than room air to treat hypoxemia. Hypoxemia and different types of hypoxia are defined. Common signs and symptoms as well as indications for oxygen therapy are listed. Various oxygen delivery devices, their uses, advantages, and disadvantages are outlined.