What does a backend do for a website?

Question

What is the purpose and which one is easiest to learn to use and implement.

Answer 1

Backend is the code that is ran on the server. The backend language connect to database, query the database and send the output to the client side.

Bakend programming language include:
PHP, Nodejs, Python and many more

Answer 2

@Luka, thanks.

Answer 3

@Wisdom I don't think that a useful site MUST have a backend. For example if your site just calculates something using JS, or if it only has single player games, the site doesn't need a backend.