Basically, every turn you draw X amount of cards (the ones on the bottom) that are played for free (save for a few exceptions). The starting cards will usually give you resources to spend on buying new cards (the set of cards on top). As your level of transformation increases, what cards available to purchase start to phase out in favor of increasingly more fetishy cards, which tend to cost more but are also generally more powerful.
The goal of the game is to manage your resources, including your deck size and TF level, and build a powerful deck in the first phase that will allow you to defeat the boss in the second phase of each round. You will need to juggle purchasing cards that bring in more resources with cards that will protect you or damage your opponent. You ideally want to get a working deck as fast as possible to keep your hand size and TF level low, but you also can't keep your TF levels too low if you want to access more powerful cards. So you have to take hits and deploy shield cards tactically to farm the cards you want before they get phased out. Some fetishes (thematic deck sets) optimally work in low TF levels and some require you to be quite transformed. The boss fight phase doesn't let you buy cards. You'll have to inflict enough TF damage or deploy enough resources (which will deal minor TF damage to the boss) to defeat them before your own TF caps out.
