You can earn credits by bringing other players to the game.

You can tell them to join by using the following link:

http://www.avirtualhorse.com/signup/YOUR #

This way the game will know that you are the person who told the new player about AVH.
When a player that you brought to AVH reaches level 15, you receive a credit.
When it reaches level 30, you receive another credit and also one credit when they get to level 50.
So for each new player you bring you can receive 3 credits, if they make it to level 50.

Note that players who log on from a computer that you used will not give you a credit, they must be genuinely new to the game.

Example of the referral link:
Gatekeeper is #1 so for me the referral link would be:

http://www.avirtualhorse.com/signup/1

For sir terris it would be http://www.avirtualhorse.com/signup/14411

So what you have to do is to replace that number with your own player #.