A few friends and I are working on a project via GitHub. We are all sharing the same branch, which may or may not be a good idea.
I edited some of the code and committed
Right now you are trying to essentially do a git merge with uncommited changes in your branch (pull is just fetch + merge). Git is rightfully complaining that such an operation would overwrite the uncommited changes in the branch.
To proceed with the pull operation you need to remove this uncommited changes from the working directory. There are a couple of ways to do this
If you are new to git I would probably start with option #1.