Where to meta write what

Hi – so great plugin. I am not well versed however in all that it does and all that I need to do. Apologies for the basic question.
I appear to have no meta stuff. Here’s what I am talking about (screenshot link) http://awesomescreenshot.com/0ba568xq76
Each tab in that section of Yoast there’s the same blank box. Is there a guide that tells me what they are for in a way that I can understand?

I have no idea if I have to do a) anything b) some of them c) all of them. And then there’s how! Any pointers, guidance graciously and gratefully received. Thank you.

https://wordpress.org/plugins/wordpress-seo/