Generate an SSH key
The key should be generated using the modern and secure ed25519 format.
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -C "firstname.lastname@example.org"
Please use a passphrase for ssh keys, even if it's not a good one.
Add to SSH agent
Make sure the agent is running. If it is, it can be added to the ssh agent: