New to programming - meta tags

I have some questions about meta tags.
1) At the top of a tab, where the title shows up, there's an image next to it. How do I add an image like that?
2) The <meta name="keywords" content="HTML, Questions," meta tag, does it still have any purpose?
3) Why is <meta name="author" content="Firstname Lastname" Used? What purpose does it serve?
4) How do you use <meta viewport>? I've researched a lot on this, and haven't been able to find anything. Thank you so much to whoever answers this :)