How do I learn all about SEO, and is there any free course or any website of SEO learning?

SEMrush provides various SEO certifications

  • SEO fundamentals - Beginners
  • Technical SEO etc

Also, HubSpot Academy provides courses on SEO

If your using a wordpress Website with Yoast plugin , there's also courses provided by Yoast academy.

You can learn complete SEO from the MOZ Seo guide for beginners.

And for SEO tips and tricks you can use SEOMaester.