After you pick any of the available adventures, the story starts.
You are taken through the story where you talk to the girl and take decisions regarding the direction in which the story unfolds.
You have 100 total energy to spend in an adventure. It can be seen at the top right corner. Answers cost energy, usually between 20 and 10, specifically.
When the energy is depleted, you can either wait for it replenish (it replenishes as time passes) or refill it with gems.