There are several types of insulin. Each type of insulin has a certain time period in which it works. In order to understand insulin action more completely, it is helpful to know the onset, peak and duration of the insulin you take.
Onset refers to when the insulin starts to work.
Peak refers to when the insulin works hardest. Duration refers to how long the insulin works. The pictures below show the examples of common insulin regimens with the action curves for different human insulins. Beef and pork insulins have a later peak and a longer duration.