The difference between Git and GitHub is as follows:-
Git is written by the creator of Linux “Linus Torvalds” which is a distributed version control system after he got frustrated with proprietary software. Git is just similar to other version control systems such as subversion or CVS, but it's distributed.
Whereas GitHub and has all the similar services which bring all of the benefits of a decentralized VCS to a centralized service. GitHub also stores a copy of your project's repository just like any other developer. If you are an absolute beginner or you have a little knowledge of GitHub in that case to learn GitHub and what is pull request or what is 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:-