You need the https:
bill@bill-MS-7B79:~/Documents$ git clone git@github.com:billb2050/bignums.py.git
Cloning into 'bignums.py'...
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
bill@bill-MS-7B79:~/Documents$
bill@bill-MS-7B79:~/Documents$ git clone https://github.com/billb2050/bignums.py.git
Cloning into 'bignums.py'...
remote: Enumerating objects: 11, done.
remote: Total 11 (delta 0), reused 0 (delta 0), pack-reused 11
Receiving objects: 100% (11/11), done.
Resolving deltas: 100% (3/3), done.
bill@bill-MS-7B79:~/Documents$