Assume you want to 'scp' from machine A to B:
A > vi ~/.ssh/id_rsa.pub
Copy all text in id_rsa.pub
B > vi ~/.ssh/authorized_keys
Append copied text to end of authorized_keys
OR
A > scp ~/.ssh/id_rsa.pub username@ip_of_B:
B > cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
B > rm ~/id_rsa.pub
