how does a plant store the sugar that it makes?

From dummies.com :

The leaves of a plant make sugar during the process of photosynthesis. Photosynthesis occurs in light (photo = light), such as when the sun is shining. The energy from the sunlight is used to make energy for the plant. So, when plants are making sugar (for fuel, energy) on a sunny day, they store some of it as starch.