1. Need to generate a local public key file from client machine
# ssh-keygen -t dsa
( from client machine)
2. Copy the file to the server
# scp ~/.ssh/id_dsa.pub email@example.com:/home/user
3. Login to the server and add the key to authorized_keys file
# cat id_dsa.pub >> .ssh/authorized_keys
4. Delete the original file you copied
# rm -r id_dsa.pub
All done, now just ssh to the server. It will login without the password.
Note : Passwordless authentication is a big security risk.