First of all you'll need to have a key pair. If you don't have one yet, take a look at the 'Generate public and private key topic'.
Your key pair is composed by a private key (id_rsa) and a public key (id_rsa.pub). All you need to do is to copy the public key to the remote host and add its contents to the
One simple way to do that is:
ssh <user>@<ssh-server> 'cat >> ~/.ssh/authorized_keys' < id_rsa.pub
Once the public key is properly placed in your user's home directory, you just need to login using the respective private key:
ssh <user>@<ssh-server> -i id_rsa