Git is a Distributes Version Control System for tracking changes in computer files and coordinating work on those files among multiple people.
It is primarily used for source code management in software development, but it can be used to keep track of changes in any set of files.
You can create remote repositories on a Git cloud provider such as GitHub, GitLab or BitBucket, and keep your code safe. This will also enable multiple developers to collaborate and work.
Checkout their respective sites for more info and tutorials.
You can download Git for Windows from https://git-for-windows.github.io. A simple Google search will help you install Git.
You can easily install using Homebrew: brew install git
You can use one of below commands based on the linux distribution:
apt-get install git-core (Debian / Ubuntu)
yum install git-core (Fedora distros)
You can use various free GUI tools such as Tortoise Git or SourceTree for working with Git.
We will see more about these later, if you face any doubt, please ask.