All websites are given a unique number when they are found by the search engines. When you website is found (indexed), it is then scanned by spider-bots (automated programs) on a periodic basis along with millions of other websites. If the spider-bot finds that other websites are pointing back to your website – this is called a one-way link - then your website are awarded a certain amount of points. Points are accumulating points in a number of ways, but this type of links to your website is most important.
In short, your quest for higher rankings in the search engines should be focussed on acquiring points from a variety of different sources on a consistent basis using chosen keywords.