You earn money based on how well you interact with Alice. The hearts that are seen when touching / teasing parts of her body come with different colors and each color represents how much she's enjoying it. When it's blue (you still earn a little bit of points, but you will not be able to progress), it means you must choose another way to get it.
When you choose to get out of the session, you will be able to get the most out of the shop.
To change the item (or the way to use the item while holding the left mouse button), you want to use the scroll wheel on the mouse, many settings are also mapped to the keyboard.