What is a web browser?

A web browser is like an empty canvas; the browser asks the server(anything can be who can give the required file), the server gives you some files, and the browser paints that file in front of you. In the same way, when you open a text file saved on your PC, laptop or phone, the OS reads that file and paints it to the text editor canvas(software).

as the OS does some mechanism to perform this task, as the same browser has some internal mechanism to do this task(loading, unloading, deleting, POST, DELETE etc)