Alright, no worries. I'm not sure where this is supposed to go, so I'll let you make the branch.

I don't know how to do this is sourceTree, but these are the steps to do it with git commands:

If you don't have anything right now, switch to master like so:
"git checkout remotes/origin/master"
Then pull it with
"git pull origin master"
now you will be on the newest master branch (I just merged this pull request into master so it has the newest versions of all of the files)
Then make your changes.
Then make a new branch with this:
"git checkout -b branch_name_here"
then commit it with:
"git commit"
then all that is left to do is to push with
"git push"

Now you should be able to come here, find your new branch and make a pull request into master! Let me know if that didn't make any sense or if you need help. I will be going over stuff like this on Tuesday too.