Search Engine Optimization helps to place you website higher in search engine (eg. Google) results.
Search engines analyze hundreds of factors to rank links but some factors are more important than others.
The following 5 factors are used by most search engines.
1. Code Architecture: If a web page isn’t coded properly a search engine could mis-rank the page.
2. Keywords: Search engines look at keywords in two ways:
a. Keyword density: the number of times a keyword appears on a page
b. Keyword placement: where keywords are placed (such as page headings, titles, bolded words, etc.)
3. Relevance: How recently the content of your site has been updated
4. Incoming Links: The number of links to your website from other websites
5. Social Sharing: Search engines pay attention if your website has acquired lots of links in social networks (if your friends have liked your site, for example).