Log on to GitHub.com and at go to your os161 repository by typing its name into the search box at the top of the page. Click on the cogwheel "Settings" icon at the top right corner. You will see the menu on the left. Select 'Manage Access'.
Scroll down to 'Manage Access' and click on 'Invite a collaborator'. In the box that pops up, enter 'UBC-CPEN-331'. Click on the UBC-CPEN-331 account that appears.
You will follow similar steps to give access to your repository to your project partner.