Hello Naila
It simply comes down to the network connection that your Linux based Git server has to the particular network device. You create credentials for a user in the device itself (either locally or via RADIUS) and then provide those credentials to your configuration on the Linux box. Then using various options such as those described in the lesson, you can access the device and manipulate the configuration as you see fit.
I hope this has been helpful!
Laz
Edited: Just a clarification. The GIT server simply stores the code. It is where the repositories with scripts and codes are kept. If however you use something like Ansible, then you create and run your code or scripts locally, then push them to the Git server to store them. More about Ansible can be found here: