In the Battle tab, you can fight Monsters with your Dragon. In order to attack a Monster, swipe across its image on your screen. The HP bar above the Monster will show how much damage you have dealt. Meanwhile, the Mana bar at the bottom of the screen shows how many attempts at hitting the Monster are remaining. Mana will become exhausted regardless of whether you hit or miss the Monster. If your attack is unsuccessful, you will see the word "Miss!" on your screen.
Once all Mana has been exhausted, your Dragon will be unable to continue fighting. If this happens, you will have two options: you can either wait for your Mana to replenish itself, or refresh your Mana instantly in exchange for Sapphires. The number of Monsters you can fight each day is limited; once this limit has been reached, you will see a corresponding pop-up message with a timer.