Fork this repository and clone to your local
After clone repo then create branch for your work
git checkout -b your_branch
Next edit your changes or add your folder
After changes your code next to add in stages type this command
git add path_file
or folder
git add path_folder/
or all changes
git add .
To adding messages if your change add commit message
git commit -m "your message"
Next if you sync to origin remote repo
git push origin your_branch
Notes: if problem for your push dont forget update your branch for upstream repo see this link
If all complete next open github and then make your pull request