As an outside user, I'd like to work on Exercise 5. But I didn't create the exercise5 repository. How can I contribute to this repository? The answer is you fork the repository, work on your changes, and when you're ready to submit them to the user who owns that repository you issue a pull request. That probably sounds like a bunch of jargon, so let me point you to some resources and give a bit of an explanation. 

When we were talking about working on projects collaboratively in class, we were talking about the situation where you and your partner knew each other and could add each other as collaborators on your github projects. This isn't always the case. Sometimes, you might find an interesting repository that you want to contribute to, but the main developer doesn't know you and doesn't want to just give you write access without checking you out first. So Github uses a fork-pull model to allow you to "fork" a repository (make your own copy of the repo which you can push to and pull form that doesn't affect the main repo---though you can also still pull changes from the original developers repo as well) and when you've got some changes you think the original user might like to add to the project, you send those changes over to the original developer as a "pull request" which says "hey, here are some changes I made. I think you'll really like them!" Now the ball is in the other developers court. They will get this pull request and they can choose to look at your changes and accept/merge them into the main repository, or they might choose to enter into a conversation with you about the pull request (and you may continue to modify this pull request until the developer is satisfied and accepts/denies it) or they might choose to ignore it entirely (c'est la vie). It's up to them. Then, depending on the main developer's preferences, they may choose to add you as a collaborator or continue to work with you via the fork-pull model. 

For the purpose of this assignment, we're going to get you to fork off the main repo (lhackman's exercise5 repo) and implement your solution for exercise5. You can then submit a pull request to lhackman. To Submit your assignment for grading you must submit a pull request with your code to the lhackman exercise5 repo, and THEN go to eclass and for the exercise5 "quiz question" tell us know what your username is. Note that if you continue to push to your forked repo after issuing the pull request, these changes will become part of the pull request. So in this way you can submit early and often, just like we always recommend! 

Some instructions/directions for forking/issuing pull requests can be found here: 
forking : https://help.github.com/articles/fork-a-repo
Pull requests: https://help.github.com/articles/using-pull-requests