A video demonstration for this topic can be found in your website dashboard, under Video Tutorials > Yoast SEO Tutorials
Provides keyword and SEO analysis, as well as tell you how readable your page or post is for users and search engine. It is similar to Page Analysis Tab.
If the item is not set to a GREEN DOT, it has an eyeball icon next to it and when you click on that icon, it will highlight the area on your page or post that needs to be adjusted in order to get that item to a GREEN DOT.
If you are unclear what adjustments the items need, you can click on one of the blue links and it will take you to the Yoast SEO blog post that explains what is being highlighted and how to fix it.
Please note that the readability analysis tab does not proofread your post or page. It won't point out grammatical or spelling errors.