The role of every search engine is to give you search results which will show you URLs that contain themes you are looking for. In user's search query,
you may type one or few keywords, or phrase, which will best describe theme you are looking for.
General search engines are useful when you are looking for general and
lightly informations, but if you are looking for specialty, detailed informations it is more useful to use specialty search engines. There are a lot of specialty search engines:
for music, pictures, marketing, e-zines, nature, science, sport, cars, ... In their search results you will get lower number of URLs, and every URL will contain certain theme, you
are looking for.