Why do people store food in the refrigerator than at room temperature?

Spoiling is caused by decomposition bacteria, that use enzymes to digest their food, in the same way that we do.

Enzymes have an ideal temperature which they work best in, which for the enzymes used in digestion, tend to be around body temperature in humans, or room temperature in bacteria. If the temperature gets too hot or cold, the enzmes cannot function as well, and it takes longer for the food to spoil.

Therefore, putting food into a fridge will slow down spoiling because the bacteria that cause the spoling cannot work as well in cold conditions.