Beacon is a small device witch emits BLE (Bluetooth Low Energy) signal in cyclic time. Beacon is powered by 3V battery. On the 2. image you can see how to insert the battery into the battery slot(+ has to be on the top site). On the 3. image you can see how to insert the beacon into the case. This step is important for emmitting good signal so make sure you have it right. How to set a good beacon position can be found in the Places course under the Positions chapter.