Skimming involves quickly reading the first and last sentences of paragraphs to get the main ideas of a text when you don't have time to read everything in detail. Scanning is searching a text specifically for a piece of information by quickly looking over headings, numbers, and names without reading fully. The document provides examples of when to skim or scan, such as when looking for a specific fact like how many sons a mom has, as well as tips for how to skim and scan a text efficiently without reading every word.