When you are in a battle, you have dice at the center of the screen. You drag them and drop them on a card to activate it.
The card's effect is written on it, and the dice it accepts are under. For example, a 4+ means a die with 4, 5 or 6.
When you're done for your turn, press the play button at the top of the screen and the succubus will play her own card, visible at the bottom right.
Status and other effects are detailed in a [?] tooltip on the card or in the help menu.
If you need more help, don't hesitate to ask, it's good feedback. I know exactly how the game works, so I something badly explained can be obvious for me, but not a new player.