To download a repository hosted on github

git clone git@github.com:account_name/repo_name.git

The git@github.com:account_name/repo_name.git will be shown on the home page for the repository on github.com

To update your code from the master branch of the repo:

git pull origin master

To commit the changes you have made locally:

git commit -m "the message explaining what these code changes did"

To send your changes to the repo at github:

git push origin master