What are SEO Title and Description for on Pages and Posts screens?

If I load any page and scroll down, I see the SEO Title and Description text boxes which fill in automatically. So that works fine. If I click Pages on the left while in the Dashboard I see all my pages. There are “SEO Title”, “SEO Description” and “SEO Keywords” columns. For every page it says “No title”, “No description” and “No keywords”. For each field there’s an edit button you can click and you get a small text box where you can type something. It’s the same for all my posts. If I load a post and scroll down, the SEO title and description are filled in. If I click Posts on the left in the dashboard I have those same 3 columns with no data for any field. What are the fields in these columns for? Am I supposed to leave them blank?