SSH authentication using keys

First you have to create a key. Although using a password to further protect your key is not obligatory, I personally very much recommend using a password:

$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):
Enter passphrase (empty for no passphrase): xxxxxxxxxxx
Enter same passphrase again: xxxxxxxxxxx
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:
xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx user@host

Then you have to upload your public key to the remote host:

$cat /home/user/.ssh/id_rsa.pub |ssh user@host "cat >> .ssh/authorized_keys"

Before you connect to the remote host, you can use the following command:

$ ssh-add
Enter passphrase for /home/user/.ssh/id_rsa:
Identity added: /home/user/.ssh/id_rsa (/home/user/.ssh/id_rsa)

This way you don't have to provide the password for your key each time you connect to the remote host.

Great page with some more very useful ssh tricks here.