I have the front-end source code, but I don’t know how to connect it to the back-end.

Question

I want to develop a backend management system, similar to cms. There are 1000 html files. I want to convert them into php or stored databases, but I don’t know how to operate them. I tried to transfer these files to the WordPress theme yesterday, but failed many times. , I would like to ask if you have any solution.