In SEO On Page is the major factor which helps Search Engines to analyze/ understand your website theme and relevance. On Page SEO is the process to modify your HTML tags and content of your website to make it more friendly with Search Engines.
Off page SEO is the activity that we do outside of our websites. It’s not about links it’s more hard and deeper. If you are depending on your website to rank in 1-10 position then On page is not enough some peoples depends on On page but is not done to rank up Off page SEO is important.