SEO is the act of trying to increase the ranking of your site within Google for specific keywords within the unpaid (organic) listings, ex. You want to go from 7th place for ‘family counselling’ to 3rd place.
Google’s become the king of search because they’re very good at determining what the best sites are for certain keywords. There are two main ways they do this. They look at ‘on-site’ factors and ‘off-site’ factors.
are things on your own website which makes google think you’re relevant for a certain term. These things include the frequency of the keyword throughout your page and in the Title tag of your website. How important the keyword seems on the page (whether it’s bold, coloured, near the top, etc.). The number of pages within your website (more reputable sites often have more pages). The age of your website. And a variety of other factors on your website.
are things outside of your website which tell Google your site is important for that keyword. Examples of this are the number of other different websites which link (a link is essentially a vote for your site since they’re telling their visitors you’re worth visiting) to your website. The keywords used in links back to your website. The quality of websites linking back to your site, and the diversity of link types going to your website. These days to look natural you want all types of links back, blogs, comments, social media sites, relevant directories, etc.
As far as importance of on-site vs off-site factors, it’s likely around 30% on-site and 70% off-site, however I’m seeing more of a shift to on-site factors lately.
Google doesn’t want people actively manipulating search results since it’s not good for their users so building links to a site must be done very carefully and on-page factors can’t seem spammy because if they are Google will penalize you and you’ll see rankings drop drastically instead of improving as you had hoped.