Generate a key with the following command.  If you are trying to setup passwordless authentication, then do not enter in a password

ssh-keygen

or if you want to use DSA,

ssh-keygen -t dsa

Example:

[root@localhost ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
ef:f2:34:e5:12:ac:ab:1b:67:9f:ff:00:12:2d:cd:16 root@localhost

Upload public key to server.  Note: you will need to enter in your Password so ssh-copy-id can upload the key, after that you should not need to enter in a password.

 ssh-copy-id root@remote-server

Now login to the remote server.

ssh root@remote-server