What does a Search Engine do?

Search engines have four main functions:

They crawl the Web (via spiders)
They index the Web documents and pages they find.
Search engines process user queries.
Finally, they return ranked results from the index.

Search engine marketing

Search engine marketing (SEM) has two arms: search engine optimisation (SEO) and pay per click (PPC) advertising. These correspond to the two types of search results.

SEO aims at improving a web site’s ranking in the natural search results. PPC advertising involves bidding for placement in the paid search results section of the SERP. Both SEO and PPC advertising are based around the same fundamental concept: keywords.

Both SEO and PPC advertising are based around the same fundamental concept: keywords.