Organisms use their energy for three main purposes: building up larger molecules from lots of smaller ones, muscular contraction, and maintaining body temperature.
Aerobic respiration is the more common type and takes place whenever there's enough oxygen, it's the most efficient way to transfer energy from glucose and it takes place continuously in both plants and animals, specifically within the subcellular structures known as mitochondria.
Anaerobic respiration is respiration without oxygen, it's used when there's not enough oxygen to follow the demands of aerobic respiration, in this case, glucose goes to form lacticacid.
Anaerobic respiration in plants and animals is different, in plants and yeast, glucose is converted to ethanol and carbon dioxide instead of lactic acid, this process is called fermentation.