Put your earbuds back into the case to recharge, a fully charged case can recharge both earbuds up to 4 times.
The LED indicator on the case shows its battery level, from green (full), through orange to red (low).
Connect the case to a USB power source via the included USB-C cable to charge it. When your earbuds are in the case, they turn off. Taking them out will turn them on and try to reconnect.