Interactive walkthrough, captured from the company’s help desk (originally an embedded Tango guide), reconstructed step by step:

1
2You'll see a "Yoast SEO" section at the bottom.
You'll see a "Yoast SEO" section at the bottom.
3
4
5This should contain the focus keyword and be a summary and hook of what your page is about. Have the length be somewhere in the green. Not too short or too long.
This should contain the focus keyword and be a summary and hook of what your page is about. Have the length be somewhere
6This saves your work
This saves your work