That is a very valid question and indeed there is little talking about that in the PDF!
But basically, you can normally bet up to your PD (power dice), thats what betting a dice means, saying that you like, bet 3 dice for example. Your PD is normally 6 but that can be altered and the actions you can take sometimes may alter that or give you specific numbers to bet. We will probably do a little patch correcting some of those mistakes.
Hope that answers your question! I'm really glad you enjoyed the concept of it!