Git is a collection of command line utilities that tract and record changes in files. Using this you could restore old versions of your files, compare, merge and analyse them.
Git is decentralized which means that it doesn't depend on a central server to keep old versions of your files. Instead it works fully locally by storing this data as a folder on your hard drive which we call as a repository. You can store copy of your repo online which makes it easy for multiple people to collaborate and work on the same code. Github and bitbuckets are supporting these functionalities.
How to Install Git
Installing Git is simple.
Linux - Open terminal "sudo aot-get install git"
Windows - https://gitforwindows.org/ offers tool for windows. Download and install it
Mac - Using brew, install git "brew install git" from your terminal.
There are some GUI tool which you could use, we will talk about this later after learning few git commands.