Iframes nevery work?

So I linked khanacademy and quora just to learn how to do an iframe and it never shows the website. Why is that?

This is now getting on my nerves as I am not allowed still to link anything so no can help.

I wil ldescribe, first I put the ifram tag and then src= and then between 2 quotations mark I copied quora link which included http and the quora websitethen closed the tag and then closed the iframe tage with a back slash. It shows only blank screen. I cant see the quora site?

Iframe refused to display website | StackOverflow