Search Engine Optimization is a process to increase traffic to a website when users search related content through Yahoo!, Bing, Google, and other search engines. It targets image search, local search, video search, content search, and industry-specific search but does not influence paid search results.
To increase relevance of specific keywords and remove barriers to the indexing activities of search engines, you’ll need to modify the content, HTML and associated coding of the website; and this process is called optimizing a website.
To attract online visitors and to be ranked higher up in natural search, it is important to make your website SEO friendly including design, images, menus, videos, shopping carts, etc.
If you are working with a CMS (content management system) to edit your website, make sure that it will handle content in a SEO friendly way.
In the article How does Search Engine Work, you will learn how Search Engine actually works.
Now, if you want to make your WordPress SEO friendly, then you need to see SEO Guide for All WordPress Bloggers, and then What to Do After Making Your Website Search Engine Optimized.