Git is a decentralized version control system with the goal of allowing developers to keep track of/revert changes, work on different versions of the software at the same time, merge changes together etc. GitHub is just a site to store Repositories online, it's not integral to git.
The place where you store your work. At first, it’s a folder on your computer. When you add version control, the folder becomes a repository and can keep track of the changes you make.
A folder becomes a repository after you init git inside it (either with the init command line command or though a GUI program). This will generate a hidden .git
folder inside the top level directory efficiently containing all the data of the changes you will make later.