400 kWh in one month is 400/30= 1.33 kWh per day = 54 Watts per hours on average. That is one electric lamp or "drain" from TVs, chargers, computers and your refrigerator.

You can buy one of those "kill-a-watt" tools and see the usage of say refrigerator or computer.

Your electricity provider (with a smart meter) may also have your usage hour by hour...