Git makes a distinction between your local repository and remote repositories. You have to commit your change to your local repo before you can push it to the remote one. So first you "git commit," then you "git push."
The total workflow goes something like this:
git clone git://nex-3.com/arc-wiki.git
emacs lib/import.arc # Make your edits
git add lib/import.arc # Schedule lib/import.arc for committing
git commit # Commit lib/import.arc to your local repo
git push # Push your local changes to the remote repo
The "git add" step is due to a little idiosyncrasy of Git where "commit" doesn't commit any changes you don't explicitly tell it to via "git add." You can also do "git commit -a" to automatically add all changes before you commit.
Also, "git commit" takes the same -m parameter that "svn commit" does.