I'm going to add a FAQ and a few more how-to's to the website in the next days. But here is a short summary about the referral program:

-Invite new users by giving them "Your personal referral link"
-You get this link by clicking on the button in your dashboard
-When a users visits steemvotes through your link, he gets "marked" for 24h
-If the invited user registers within these 24h, you (the referrer) will receive 50 credits
-You can invite as many perople as you want, there's no limit
-You will only receive credits for NEW users