Submitted or crawled page URL addresses are then queued for a spider to visit and retrieve for indexing. Every engine does this a little differently. The spidered page is then run through an algorithm at the search engine, which determines word weight and relevancy, and many now also look at link popularity. The algorithms are very complex and are never made public for obvious reasons. The greater the relevancy of a page for a particular search term, the higher in rank it is displayed in the results shown the searcher.
Every search engine uses a different algorithm to rank pages.
As a result, it can be difficult to have a page rank well on many engines. What is considered as very relevant by Alta Vista may be considered far less relevant by Excite and rank considerably lower for the same search keywords. These are built to target specific keywords and keyword phrases for specific engine algorithms. Usually these pages have a link pointing to your main site, so that when they are found in search results the visitor sees the doorway and either clicks through to your main site or moves on. This bears a little explaining.