I was wondering what does it mean by basic secretion of insulin and by the postprandial peak on the secretion of insulin?

Insulin: Hi. The body needs some Insulin even when you're not eating in order to prevent breakdown of muscle and too much release of fat from fat cells and glucose from the liver; this is called "basal" Insulin (not "basic"). When you eat, you need a burst of Insulin to manage the caloric burst of the meal and to clear glucose (and indirectly, fats) from the blood (prandial insulin) and store them.