and then when i type git push origin master,
after entering my passphrase, i get:
ERROR: gabaluschi/first_app.git doesn't exist. Did you enter it
correctly?
fatal: The remote end hung up unexpectedly.
That's saying you've already added the remote. It looks like there's a
typo there though, since it should be github.com (not github, unless
you've been messing around with /etc/hosts or your ssh config), which
may explain the second part. I'd try removing the remote & trying
again (although as Peter says, this is really a git question not a
rails one)