Google has developed automatic algorithms that rank your site. They send out what are called “spiders” to “crawl” your site and check it for over 100 indicators that determine whether your site is valuable or useless. These indicators include things like backlinks, domain age, traffic, fresh content, etc.
SEO is the art of making sure those spiders are happy with what they find. It is an extremely complex field that is constantly changing but in all that chaos there are a few constants that have remained true since the beginning. I’ll talk about those here.