This will explain, how you can keep your own changes on top of somebody elses git-repository. We will utilize git rebase for this.
Here i'll use a bogus project which does not exist, but you can paraphrase from it.
First you clone the repository:
git clone email@example.com:foobar/baz.git
After that you change into the repository:
Now we create our own branch which tracks master:
git branch -t mybranch
Since we don't want to modify master, we check out the new branch:
git checkout mybranch
And since it helps me, i often remove the local master-branch:
git branch -D master
Now whenever you make changes, you simply commit them to your mybranch branch. When you're done and your upstream has released a new version, you simply rebase like this:
git rebase origin/master
If there are conflicts, it will ask you to resolve them manually if it is not able to do so by itself. If this happens, simply edit the file so that the conflict is resolved and add it with git:
git add conflicted/file.c
When you're done editing, simply run:
git rebase --continue
Saving your changes to your own Repository
I find it useful to save my changes somewhere else than my workstation, not only for backup-purpose, but more or less access control, if i ever have to team up.
git remote add mygit git@mygit:myrepo.git
and start pushing to it
git push mygit +mybranch
Hope you find it useful.