Bee feeders are used to supplement a hive at various times of the year, to improve its viability. Beekeepers often feed their hives in the spring upon installation of a new package of bees, or in the fall if the colony is low on honey stores.
Most beekeepers feed 1-to-1 sugar water in the spring, and 2-to-1 sugar water in the fall. We recommend pouring pure cane sugar into the bee feeder and then adding hot water while stirring with a spoon until the sugar dissolves. If you've got honey from hives you trust, you can also feed honey to your bees.