A search is the organized pursuit of information. Somewhere in a collection of documents, Web pages, and other sources, there is information that you want to find, but you have no idea where it is. The NASA search engine gives you the means of finding that information.
You conduct a search by issuing a query, which is simply a way of asking a question that will find the information you are looking for. Searching is usually an iterative process. You submit a query and if the results list does not contain the information you are looking for, you refine the query until you locate a page that contains the answer.