Does the right or left AirPod work by itself? Do I need to use both AirPods together?
Yes, AirPods are designed to be used individually or together.
Place just one of the AirPods in one ear and they will automatically detect what's happening. When one AirPod is in use, it converts stereo sound to mono for the best listening experience.
Each of the AirPods has its own battery, and they are independently managed. For example, one AirPod can be used for making phone calls, which will extend battery life overall.
When the second AirPod is placed in your ear, the headphones will transfer to stereo mode automatically.