Within your .env file you can set environment variables, which is done in a KEY=VALUE format, e.g.

SECRET_KEY="hello_world!"
OTHER_SECRET_KEY=hello_world_again!

You should be able to use a programming language to manipulate environment variables. In python try:

import os
print(os.getenv('SECRET_KEY')) # Prints "hello_world!"
print(os.getenv('OTHER_SECRET_KEY')) # prints hello_world_again

In node.js

console.log(process.env.SECRET_KEY)) # Outputs "hello_world!"
console.log(process.env.OTHER_SECRET_KEY)) # Outputs hello_world_again

Note that quotation marks will be part of your environment variable (unlike in python or node.js where the interpreter assumes that this means your variable is a string). So H="H" means that h is assigned the value of "H" not H.

The .env file is hidden from other users, who cannot see it when they look at your repl. It is not included in forks that other users make of the repository.