The three main elements of SEO are:
Technical SEO.
On-page SEO (or Content SEO)
Off-page SEO (or Links)
1. Technical SEO
Technical SEO encompasses issues that relate to the website infrastructure, clustering, and categorization, internal links, page speed, sitemaps, etc. These factors directly relate to Google's capabilities to crawl your website.
2. On-page SEO (or Content SEO)
On-page SEO or keyword optimization is the process of fine-tuning a good piece of content for the Google algorithm. It is called on-page SEO because it is happening ON your website where you are in charge and able to make all of the required changes.
3. Off-page SEO (or Links)
Off-page SEO is the process of improving external ranking factors that are outside of your control. The main off-page ranking factor is backlinks. It also encompasses soft factors such as brand mentions, social shares, or consistent entity details (name, address, phone number) and reviews.