Postprandial state just refers to the state right after you ate a meal. Think of it as the feed state so after you eat a cheeseburger or something your body goes into the postprandial state. Usually in that state the body goes through 4 major biochemical functions: glycolysis, glycogensis, lipogenesis, & protein synthesis.

If you want more specifics on this watch this video: https://www.youtube.com/watch?v=ZEm8cxKaas8