What is the difference between Requests and Selenium?

Question

Python

Hello!
After reading about Selenium and using Requests a little, I still have a couple of questions:
1) What is the fundamental difference between Selenium and Requests?
2) What can Selenium do that Requests can't?
3) Why do I often see codes where Requests is used in conjunction with Selenium?
4)(Example) Is it possible to login, click, upload a file on a site (instagram, etc.) using only requests?
Many thanks in advance for your replies

Answer 1

docs.python-requests.org can't click, it can send and receive http requests
Selenium is a wrapper for the browser api through which you can click. It can do everything a browser can do

Answer 2

Requests is a library for making requests. It is more "low-level" and may not be able to cope with JS sites. But much faster than Selenium,
Selenium - This is a whole combine, in fact controls the browser and can do almost everything that a browser can do, including working with JS. But in terms of speed, it is much inferior to Requests, because the whole browser actually works.