These generally operate using massive databases that regularly search the web looking at the titles, keywords, descriptions and content of pages. The database then attempts to match its findings with whatever parameters you enter as the search term. As you might imagine, the explosive growth of the Internet makes the indexing of it a rather difficult and ever-shifting task. Different search engines will offer different results. It might be said that searching the web is more of an art than it is a science.
Some people can simply do it better than others.
Try to plan your search so you don't get distracted. Think of different ways of phrasing your search. Read the help and information pages at your favorite search engines. Don't get stuck on a single search engine for every search. Here, then, is a list of the search engines that we at TIS Training use frequently.