Skimming is reading quickly to take in the main idea of the content without seeing and absorbing every word. When you skim, you get the gist of what has been written even if you don't recall every detail. Flipping through your morning paper is an example of skimming; you are not looking for anything in particular and don't have time to read each column or article with focused attention.
Scanning is similar to skimming, although you scan when you are seeking specific information. You are only interested in that information and disregard the rest of the text. Examples of scanning include reading a TV schedule or a restaurant menu.
Reading novels for fun falls into the category of extensive reading. You read more slowly, with in-depth focus, with the goal of gaining a broad comprehension of the text. Extensive reading is a skill for acquiring general knowledge. You employ extensive reading when you find a magazine article about a topic that interests you.
Acquiring specific, accurate information is the goal of intensive reading. If you follow a recipe, you read it intensively. Intensive reading involves focused attention, retention of information and accurate detail extraction. Other examples of intensive reading include reading textbooks, contracts, insurance claims or affidavits.