Automatically

Command to add a system automatically to the authorized keys file to be able to login without a password

ssh-copy-id username@remote_server_ip

Manual

Manually add a system to the authorized keys file to be able to login without a password

mkdir ~/.ssh
touch authorized_keys

echo "public_key_content" >> ~/.ssh/authorized_keys

chmod 600 ~/.ssh
chmod 700 ~/.ssh/authorized_keys