When you classify or put an individual thing in a group, you are telling the reader (or listener) that the individual item shares the characteristics of the group. This is not to be confused with stereotyping, in which one shared all blondes or all jocks or all A is used to assume knowledge of everything else about the individual.

We need to classify by important characteristics. I have a brother and I have a plant on my desk. If I classify them both as living things, I probably won't have said anything very useful.

They don't share enough other characteristics. I have a brother and I have a sister. If I classify them as members of my family, a large number of shared characteristics is now implied. Remember that we're always choosing patterns and methods of development in response to the purpose of the writing or other communication. A few methods of development ago, we left behind some sport utility vehicles. Let's go back and get the Bronco. It doesn't want to start in the morning, especially on wet, cold mornings. The mechanic tells you this is probably an electrical problem. With that classification (made in the form of a diagnosis), you and your mechanic know where you should look first for the problem and the solution.

When you develop an idea by classifying, the details you use will probably be the characteristics of the group in which you've placed the ideas. To say, This is a problem for Superman, means it's a huge problem, local law enforcement agencies can't handle it, the armed forces can't handle it, and the combined resources of everybody present wouldn't be enough to solve the problem.

The threat or problem, whether it's a meteorite, a tidal wave, an earth villain, or an alien invasion, is one that will require super strength, super speed, and invulnerability.

You probably don't write that much about superheroes, but you will be asked to write about other topics that can be developed through classification. If you classify a book as young adult fiction, or a rock as a sedimentary rock, or a cleansing solution as a bactericide, or a sandwich as a veggie-burger, you let the reader know some characteristics of the individual thing by the group you say it belongs in.