Web Application Full Stack Frontend + Backend

I feel like a bit of a nonse to be honest at the moment. I'm trying to build an application on github but I now want to start trying to tie in the backend. I suppose what I'm struggling is trying to get the architecture right in my mind so I know what i'm doing 100%.

When building a full stack application, I've seen some people creating the static version of the frontend and then tieing it into the backend and I suppose its confusing me a little bit. If you think of wordpress, you have the front, and then the backend admin area.

Anyone able to understand where I might be coming from?

Anyone able to advise, maybe on a workflow possibly to look into? Any information much appreciated!

Kind Regards,

Bridget