Logic is simple.

Want to check items
Such as mana available, cards in hand and the order to play cards.

So check you have enough mana with condition rules,
then with gain rules, get it to give higher gain to card A to play first, then 2nd card check if card a is in play then give higher gain to cast for that.

Hope that helps.

That refers to cards with Combo such as bandit. Which give added affect if card has been played before. Not combo as you are thinking