You can read about the techniques used in The Search Engine Watch . The other way is to use humans to index and to classify pages. The best known example is Yahoo . There is another human indexed directory which is the Open Directory . The Open Directory is interesting because its results are available free to anyone who wants to use them and it is staffed by volunteers.
People become editors by applying to look after a category of links.
You can apply to become an editor. This is the Web at its best, combining the efforts of volunteers to make things better for all. The next step will be to add in Reputation Manager assessments . Search engines are becoming better at finding relevant material. Some of us are obsessed with measuring things.