On-page SEO covers the tactics you use on your site that help search engines better understand your content and rank you. All of this is included in on-page SEO, content creation, title tag optimization, image optimization, and much more. Off-page SEO includes activities from or behind the scenes of your website. Off-page SEO involves all the actions you take to impact your search engine rankings that fall outside your website.
This may include creating backlinks, being active on social media, and blogging as a guest. On-page SEO involves all the on-site techniques you can use to ensure that a web page ranks in a SERP. It can also help determine how well that page ranks.