Given that you are a Gentoo user (I used Gentoo for two years, now use Kubuntu), you should have no problem using git from the command line. I do most of my git operations from the command line, but occasionally use GUI programs to get a visual representation of the repository.
The way Git works is it is a distributed revision control system, there is no central repository where the code lives. Each developer has a full copy of the repository. With this repository, you can push your changes to other developers, or pull their changes in. Hopefully this isn't confusing, but GitHub takes this idea and introduces a central repository. So when you create or fork a repository, you create a central repository. Then when you clone this repository, you create a local repository. So if you do a git commit, it just goes to your local repository. You have to do a git push, to send your changes up to your repository on GitHub.