A good explanation about what GitLab actually is can be found HERE.

If you already now you way around you can log in to our server on this address: https://gitlab.asc.tuwien.ac.at/. If you only want to look at existing content you can already do that. Just create your account and log in. If you want to host your own projects please get in touch via admin@asc.tuwien.ac.at to unlock this feature for you.