Why can't I add more sections while customizing my Brooklyn theme?

I posted this in the theme section but I think I should have used here instead so I redid it.

I am using the Brooklyn theme. No edits to code.

I have used shopify for several stores. I went on a break from it about 2 months ago, and just started a new store. I remember being able to add a lot more whilst customizing the pages on the admin section as well as theme section, but it has no option to do anything now. This is what I see. Am I nuts or didn’t it allow you to add more sections and things to the page before?

Under this little section it also has options I have never seen before. It says “default, Full width, contact”

Is it just the theme I chose? I need to add some products and info to that page. Or whatever else like text boxes and such.

Thanks in advance for anyone that can tell me what I need to fix!