How to register custom shipping gateway?

I'm trying to build a custom shipping gateway.
The process I have followed is to take the file of an existing gateway, copy it, change its filename and alter its contents to suit my needs. So now I have a new file called mp-my-shipping.php inside the marketpress-includes/plugins-shipping filder.

The question now is:
How do I tell MarketPress "hey, you've got a new shipping gateway, please include it"?