Github

Create pull request

Start a new branch:

git checkout -b <branch-feature>

Do modifications (it is ok to checkout new branch after some local changes where made but before the first commit).

Then, add changes:

git add .

Commit and push to new upstream branch:

git commit -m "Add feature X"
git push -u origin <branch-feature>

Navigate to github.com and open new pull request (be sure to select the correct upstream branch!).