Explanation
To log into a remote SSH server using SSH keys, the client needs to generate a public and private key pair using the ssh-keygen utility. The private key (~/.ssh/id_rsa) should be kept secret and protected by a passphrase, while the public key (~/.ssh/id_rsa.pub) should be copied to the remote server's authorized_keys file (~/.ssh/authorized_keys) using the ssh-copy-id utility or manually. The authorized_keys file contains the public keys of the clients that are allowed to log into the server using SSH keys. The client can then use the ssh command with the -i option to specify the private key file to authenticate to the server without entering a password. References:
LPIC-2 Exam 202 Objectives, Topic 212: System Security, 212.3 Secure shell (SSH) (weight: 4) How To Configure SSH Key-Based Authentication on a Linux Server How To Configure SSH Key-Based Authentication on a Linux Server