I will tell you this with an example which will let you understand it. Assume you and your friends are programmers. You are staying somewhere else and away from your friends.
If you come up with an idea of any software and you inform your friends about it. They also agree to work on it and you guys will be doing this project together. But all your friends are on the different corners of the world. It will be very tough for you guys to work on it. So here GitHub rescues you and it gives you its platform where you guys can work on together. Whatever work you do you will update your work there and same your mates will do and this will keep your code interactive to each other. To know more about such kind of things whether if you are an absolute beginner or you have a little knowledge of GitHub in that case to learn GitHub and all its concepts such as pull request or creating a repository in detail which is necessary for a programmer you can learn it by taking up the GitHub training course. If you like to read then you can have a look at the GitHub tutorial. If you want to learn it by watching the video tutorial then you can have a look at the following tutorial:- .