Motivation: I want to acces to my Bluehost server from my local computer, make some file copies ‘scp’ but from a script executed by Crontab, so I don’t want to introduce my password manually.
Solution:

• Generate the key from your local machine (I don’t think it’s needed but, store the keys in ~/.ssh
  1	ssh-keygen -t rsa

  ssh-keygen -t rsa

• Copy the public key to your server:
  1	scp .ssh/id_rsa.pub username@server_name_address:.ssh/authorized_keys2

  scp .ssh/id_rsa.pub username@server_name_address:.ssh/authorized_keys2

Source: ciberciti