If you already have a website then you are already doing some form of search engine optimization (SEO) even if you are not aware of it.  Any time you write content around a specific subject, you are optimizing that content.   For a casual reader it should be obvious that the content deals with the subject that you have chosen.  If it isn't obvious, then it isn't optimized.

A search engine also reads your content in order to (partially at least) find out what your page is talking about.  Optimizing your content requires that you focus that content around a very tight subject.  Content Optimization is only one small part of the broader SEO field.

SEO encompasses two main elements - On Site (changes to the physical website) and Off Site (anything that does not change your website).

On Site Search Engine Optimization is what we have been talking about - focusing your content around a specific subject.  It gets deeper than this for sure and I can talk about all of the on site techniques such as w3c validation, internal linking, keyword density and more in other posts.  For now, lets just focus on content because that's really what it is all about.  If you are writing good content that is focused on what people are looking for, you are doing a wonderful job with the foundation of your SEO.

Off Site Search Engine Optimization really focuses on two factors - generating incoming links from other sites or social media sites and building incoming traffic from other sites.  The techniques for this off site search engine optimization are very organic in nature.  If you write good content and let people know about that content, then they will write about your site in blogs, social media sites, other sites, reviews or other sources.  This builds link relevance, lets the search engines know about your site and also sends in direct traffic - a triple win.  For someone doing their own SEO, focusing on blogging, social media, and participation in online communities is key and will get good results.