OK, How Does SEO Work?

SEO, which is short for Search Engine Optimisation, works by making your site "friendlier" for search engines such as Google to list in their index.

No-one knows for sure just how many pages Google has indexed. It gave up posting that figure some time ago as it's irrelevant to the average internet surfer - we only want relevant results when we're searching and don't really care about the literally millions of pages that were discarded on the way.

As website owners we only really care about our pages being found for searches that are relevant to our website. And that's what SEO is all about.
Google and the other engines don't disclose precisely how they decide which sites rank at the top of the results for any given search phrase. That would be like Coke revealing their recipe or KFC listing their herbs and spices. Instead, we have to use other tools to find out how SEO works.
In a nutshell, a search engine has to make a snap decision about what a page is all about. So, if a page mentions a monkey, the search engine has to interpret whether the page is about a monkey as a primate, a monkey as a British slang term for £500 or maybe a monkey wrench as a tool. SEO works by helping the search engines with that decision.
Google tell us some of the things they want us to do to help them:
Title tags. These are the the headline the searcher sees when they get back the search results and they should be much like a newspaper headline, giving everyone a snapshot of what the page is about.
Heading tags work much the same way. The first, H1, tag is likely to be the same as the title of the page. Other heading tags work in a similar way to sub-headings in a newspaper, helping draw a reader through the page. Lazy readers ought to be able to tell most of what a page is about just from reading the headings. This article doesn't work like that, although I've bolded some items. But if your web page can tell a story with headings alone, the search engines will have a much easier job of working out what the page is about.
Inbound links: these are the search engine equivalent of a vote. Each link pointing to a page has a few words underlined and search engines take note of these words when they decide where to rank a page. So, if you search for the words "click here" in Google, chances are that you'll see the Adobe site at the top of the results. Not because Adobe want to be number one for that phrase but because so many sites use those words to tell their visitors where to get the Adobe Acrobat reader.

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Sometimes you have control over the wording used in your inbound links, sometimes you don't. But this example shows you how important the words used on these links are - they are telling the search engines what your page is about, in as few words as possible.