Open the Energy tab. You see:
- Right now: the power of everything that is on.
- Per day, week or month: how much energy was used and what it cost.
- Biggest users: which rooms and devices use the most.
The numbers are estimates based on how long each device was on and the power in watts you entered when you added it. For better numbers, check that each device has the right watts (edit the device in More → Rooms). The price per kWh and your currency are set in More → House settings.