Empty homepage text box, content edited through “Customize” button.

I recently branched into writing SEO with the Yoast SEO plugin, starting with the homepage. I’m not sure if this is the right place to ask this, basically, I noticed that the text box of my “homepage” was empty. Well, it was first filled with something like, “This is your homepage, this is what people will see when first visiting your page” or something along those lines. Not certain exactly what it said, I since deleted it when beginning to work on my SEO. So like, the actual box where you fill your homepage with text was empty and the content on my homepage is built through the “Customize” button while on the site. I’m assuming this is theme related (Using the Zerif lte theme)
Is every theme like this? Like is the content on the homepage/frontpage only edited by actually customizing it, not what you add into the text box on the page itself.
I realize this sounds extremely confusing but basically, I was wondering if this can be a good thing because I can put essentially any writing or images I desire, to help increase my SEO results.
I’m not sure if what I am even asking makes sense,
here’s an image

SEO / Theme Help

All that was text I put with an attempt to make the SEO little bubbles green and not red/orange. For my focus keyword, and readability.

So are most theme’s like this? is my main question basically.

The page I need help with: [log in to see the link]