The 'Permission denied (publickey)' error is a common issue with SSH authentication, indicating GitHub doesn’t recognize your SSH key. First, check if an SSH key exists on your machine by navigating to `~/.ssh/` and looking for files like `id_rsa.pub` or `id_ed25519.pub`. If no key exists, generate one with `ssh-keygen -t ed25519` or `ssh-keygen -t rsa -b 4096`, and then copy the key using `cat ~/.ssh/id_ed25519.pub` (or `id_rsa.pub`). Next, add this key to your GitHub account by going to *Settings > SSH and GPG keys > New SSH key*. Paste the copied key here, naming it for easy reference. Now, configure SSH on your machine by running `ssh-add ~/.ssh/id_ed25519` (replace with your key filename). Test the connection by running `ssh -T [email protected]`; a successful connection message should appear. With the key added to GitHub and configured locally, you should now be able to push without permission issues.