You can find what is called your SSH public key by running the following and copying the output:
cat ~/.ssh/id_rsa.pub
The above should succeed if you're running commands for this lab on your laptop and you created an SSH key there for lab 1. If, however, you're connected to your virtual machine and running commands there for this lab, you need to generate an SSH key on the virtual machine. (Creating an SSH key on your laptop to connect to your virtual machine is different than creating an SSH key on your virtual machine to connect to other services, like GitHub).
So if cat ~/.ssh/id_rsa.pub fails, try creating an SSH key first
before retrying by running ssh-keygen and repeatedly hitting ENTER
to accept all the defaults (including an empty password).
After you've copied the output from the terminal, go to https://github.com/settings/keys and click "New SSH key".
Name the key "cs320-vm" (or whatever you like, really) and past the
contents of id_rsa.pub to the "Key" box, as in the following
screenshot:
Click "Add SSH Key" to finish adding it.