To be listing in Google Search, there are two ways to do it. Pay and get listed or Raise the Website Ranking.
In the beginning of days, they all originally just tracked Keywords. The website which had those keywords were ranked higher and displayed in the first pages.
Search engine today, all follow the model of the website which are refereed by other websites(Backlinks), to be ranked top in the list. “Keywords” lets Google/Search-Engine see the website. And “Backlinks” lets Google/Search-Engine know how much to trust the website. Keywords are important, but Backlinks help move up the Website Ranking.
There are two aspects to it, how search engine find and rank pages. First is ON-SITE Components, which includes optimize website to contain keywords which are relevant to what the website is about. Second is OFF-SITE components, which generates backlinks to the website which originate from other sources. This is done through Articles, Social Media, Blog Posts, Discussion Boards, Etc…
A good SEO takes time, so sooner we start, the better it is