how generate ssh keys and copy to server

ssh-keygen -t rsa
save generated keys to /home/user/.ssh/ directory
will be 2 keys - id_rsa (private) and id_rsa.pub (public)

copy pub key to the VPS:
ssh-copy-id -i /home/user/.ssh/id_rsa.pub root@XXXXXXXXX

after successfull copy need change SSH config on server:

nano etc/ssh/sshd_config
and change 'PasswordAuthentication yes' to 'PasswordAuthentication no'
CTRL+O

sudo systemctl restart sshd.service

ssh -p 22 -i /key username@XX.XX.XXXX

login to ssh with keypair.