$ git clone https://github.com/YOURID/mytestrepo.git
$ nano solution.sh
# or some other tool (e.g. emacs, textedit, vi, ...)
$ git commit -m "I updated the solution"
$ git push
# git push will request your github ID and github password
$ nano newfile.py
$ git add newfile.py
$ git commit -m "I added this new file" newfile.py
$ git push