The Flow Frame consists of partly pre-formed honeycomb cells. The bees complete the comb with their wax, fill the cells with nectar, which they turn into honey, and cap the cells as usual.
The Flow Key is inserted into the top operation slot of the frame and turned 90°, the cells split vertically inside the comb forming channels, allowing the honey to flow down to a sealed trough at the base of the frame and out of the hive (a bit like a tap). During this operation, the bees are undisturbed on the comb surface.
When the honey has finished draining, the Flow Key is inserted into the bottom slot and turned again. This resets the comb into the original position, and allows the bees to chew the wax capping away and fill it with nectar to repeat the process again.