SEARCH ENGINES are websites which list links to multiple other websites based upon key word criteria you specify. In most cases, you will want your website listed on as many search engines as possible
What is a Search Engine?
Some search engines charge for listings, others accept listiing submission without fee
Because any single search may return thousands of links grouped 20-30 per screen, it's most desireably to be listed among those on the first or second screen.
Each search engine followed different rules when determining rank (where your site is listed relative to the qualifying links).