I'm glad you like the look and sound of the game, and I'm sorry the manual didn't help you out. I know that UI is one of those things I need to focus on next time.
Just for clarity, the idea of this single-round combat system is that you roll dice to form a dice pool, then open the monster's combat card and try to fill in as many "dice slots" as possible. Clicking on a die and then clicking on a slot will fill it; right-clicking a slot with a die will return it to your pool. When you confirm your selection on the monster's combat card, empty slots penalize the player with damage, curses, or less XP or money. The puzzle is to fill as many slots as possible.
You start with one spell called "fuse mana" and you learn more on your adventure. These spells allow you to manipulate the dice in various ways, by spending dice as mana to gain, change, or reroll dice in your pool. Manipulating dice will help you solve the puzzle of filling in the monster dice card.