Before creating a new branch, pull the changes from upstream. Your master needs to be up to date.
Create the branch on your local machine and switch in this branch :
$ git checkout -b [name_of_your_new_branch]
Change working branch :
$ git checkout [name_of_your_new_branch]
Push the branch on github :
$ git push origin [name_of_your_new_branch]
When you want to commit something in your branch, be sure to be in your branch. Add -u parameter to set upstream.
You can see all branches created by using :
$ git branch
Which will show :
* approval_messages
master
master_clean