Create new branch

From the Git Command prompt

git checkout -b TestBranch

the output should be something like

amit@amit-desktop:~/dev/code/courtres$ git checkout -b TestBranch
Switched to a new branch 'TestBranch'

Do the code change

Use an editor to make the code changes.

Commit and push your changes

Add the changed file to index

git add README.md

Commit the code

git commit -m "Test Change"

sample output

amit@amit-desktop:~/dev/code/courtres$ git commit -m "Test Change"
[TestBranch d7201f3] Test Change
 1 file changed, 2 insertions(+)

Push your local branch to remote

git push -u github TestBranch

Creating a pull request

https://help.github.com/articles/using-pull-requests/