Using Yoast with WordPress site. When I add SEO, it flags evey page red

I am new to building websites and have no idea about SEO. I have a WordPress website and am using Yoast to add SEO. I’m editing each page, however, every single one is flagged in red when I have added keywords etc. and update them. It doesn’t really explain what I’m doing wrong and what I need to do to increase the ‘score’.

Is anybody able to help me with this and offer some constructive feedback?

Thank you.
Louise