Front-end routing and back-end routing?

  node.js, question

I just started to learn nodejs recently, and I am not quite sure about the front-end and back-end routing. Please ask the great god for help.

The front-end and back-end separation is now advocated, and the back-end only provides data API. Then the problem arises. What is the use of back-end routing?

Receive front-end request url

For example, the address bar at the front end iswww.xxx.com/show;

This address may requestwww.xxx.com/aaa;

Then what is received by the backend iswww.xxx.com/aaarather thanwww.xxx.com/show