My wife keeps bees and had a hive opening and meeting at our house this weekend.
Here a frame is inspected. This frame has a lot of capped honey cells.
The first part of the season you allow the hive to build itself up. Then you add extra frames on top with a mesh that excludes the queen but allows workers through. As natural hoarders, the bees will begin to store honey in the frames that the queen can't get to.
The queen excluder prevents her from moving up to lay eggs so that only honey is stored there.