How to set up .htaccess to serve both angular and php from the same host?

Question

Apache HTTP Server

I want to make the client-side angular from the same host from which the php backend is distributed. Something like this: there are frontend (with angular) and backend (with php) folders. I want index.html from frontend to be on localhost, and backend to be somewhere around localhost/api. How can you set it up like that? I don't understand how to configure this .htaccess at all. Everywhere it is so difficult to describe it in Google ...