In order to access any repository you will first have to update your terminal. Input:

sudo apt update && sudo apt upgrade -y

Now, to install the regular GitHub Repository, Input:

sudo apt install git -y

After installation, you will need to set up standard settings such as names and e-mails, mainly around git commit messages. This is pretty straightforward, as the tutorial will explain below.

The first step is to provide your name that will be set Globally.

git config --global user.name "YOUR NAME"

git config --global user.email "YOUR EMAIL"

mkdir example-directory -p

cd example-directory -p

git init

Now you will see a terminal output stating the status of the directory being initialized, and you can additionally see the content using the following command. 

ls -a .git

git config --global credential.helper cache

Another option you can use is the official repositories list from debian.  [LINK - https://wiki.debian.org/DebianRepository]