A search engine service provides a searchable database of Internet files collected by a computer program, called a wanderer, crawler, robot, worm, or spider.
Indexing is created from the collected files, and the results are presented in a schematic order.
There is no selection criteria for the collection of files. When you have a narrow or obscure topic or idea to research. When you are looking for a specific site. When you want to search the full text of millions of pages. When you want to retrieve a large number of documents on your topic.