It includes techniques that help your website rank higher organically in search engine results pages (SERPs). Higher the rank of website, the more people will see it thus increasing the traffic to website.
Search engines have algorithms that determine which web page will hold which position in search results based on the most relevant information they contained, and those pages are ranked higher among the search results.
Keywords, meta descriptions, and links, are some of the SEO techniques through which your content will stand out to search engine algorithms as relevant information.