I wanted to learn Javascript for my site form and input validation?

Try to finish the course and see if the content is valuable for your purpose. If it isn't keep learning in another site. 

That's a broad and unspecific request. I can tell you that KA's teaching has very little about form validation, but there are a few things about it in the HTML/CSS/jQuery course.

Try starting here:

https://www.khanacademy.org/computing/computer-programming/html-js-jquery/form-processing-jquery/a/process-forms-with-jquery-intro

Thank you so much for this guiding link. I start learning. And this is very helpful for me. I hope I will be able to input forms validate for my site saudi national day 2021. Appreciation.