GIT sample flow:

Take a Clone:
git clone "https://www.mysite.com/user/repo.git"
Checkout the branch:
git checkout branchname
Add remote:
git remote add upstream "https://www.mysite.com/global/repo.git"
Fetch Latest:
git fetch upstream
Merge latest to your branch:
git merge upstream/branchname branchname
Commit your changes at this point...then push local changes to origin
git push origin branch

Now create a Pull request from UI



Notes:

Keep a set of ignore patterns:

git config --global core.excludesfile ~/.gitignore