Create the config file in your .ssh directory if it doesn’t already exist.

touch /home/pat/.ssh/config

Open the file and add your configuration:

Host xmp
HostName example.com
User username
Port 2222

Where Host is the name of the shortcut. You can also add other options like

PubkeyAuthentication yes
PasswordAuthentication no
ServerAliveInterval 25
ServerAliveCountMax 150

or another Host to your configuration. Take a look at the ssh_config manpage for more options.
You can now use your shortcut with

ssh xmp