This is an extremely brief introduction to SEO. It aims to inform you what SEO is, but not to teach you how to become an SEO expert. Much of the SEO process is just hard work and learning from your errors.
If you do your own SEO you will still likely want to chat in SEO forums and read books on the topic before starting. Many of the print books can go quickly out of date, but if you ask around there will likely be at least a couple good guides which are commonly recommended.