First, it is important to understand how search engines (like Google, Bing, Yahoo!) operate and how people perform their searches, because it directly correlates to the importance of SEO-friendly content on your website. Since Google is the most widely used search engine, I will use them as an example.
After a website has been launched, Google scans the code of the site and indexes it. Indexing is the process of creating indexes for record collections. Google uses this process to organize the massive amounts of information acquired while continuously scanning or “spidering” new and existing sites. This method allows Google to retrieve specific information quickly when called upon.
When a person performs a specific search, they use keywords to try and narrow their results in order to find what they need faster. Almost instantaneously, Google reviews these keywords and combs its massive database indexes to find matches to those keywords. Once matches have been found, Google returns only the most relevant results called SERP’s (search engine results pages).