Communicating with backend

Hey, I'm a newbie web developer and about an hour ago I've deployed my first project (yay). The project is REST API so I've developed basicly client-side and server-side seperately. So I want to ask few questions: 1. Are the client-side and server-side suppose to be completely seperated? So far I've flask's basic route function:

def main():
    return render_template('index.html')

Does it match the definition of REST api (because I only render_template once) or it should be completely seperated? 2.How do I find the server-side app address? so far the HTTP requests aren't working because it sends them to the local machine I've used to develop the project.

Thank you.

I don't really know what you mean by separated here. Client and server are inherently separated - the client runs on one machine and the server runs on another. The server app's address is shown at the top of your web app configuration page.