What is Energy?

Getting a little scientific, let's start with a definition.

Taking an analogy, think of humour in words. A joke is just a set of words, but we find them funny. We might call that a property of those words, but you can't see, hold or feel it. Like words being funny, energy is a property of something that's not observable. We call that an 'indirectly observed quantity’.

Energy is the capacity of a body or system to do work.

Instinctually we know what physical work is. Climbing stairs, lifting a box, pumping water up a hill. Work takes energy. It's never all useful - we waste some and it ends up eventually as heat.

Putting Some Scale to Energy

What are our home's sources of energy? Most often (and particularly in urban areas) they are piped natural gas (methane - CH4) and electricity down the wire. In rural areas and indeed across vast areas of Canada, the gas network may not exist. Propane tanks or heating oil tanks take the place.

How much energy does this represent? The most common unit of home energy considered is the kilowatt hour (kWh). That is, one kW of power (1,000 Joules per second) being run for one hour. kW x hours = kWh. It is usually reserved for electricity and is the unit that appears on your electricity bill. However it represents a number of Joules of energy - 3.6 million of them. As a convertible term we usually then call it an equivalent-kilowatt hour or ekWh.

I cubic meter of natural gas contains about 10.6 ekWh (38 million Joules - it depends on where the gas comes from).
I litre of gasoline contains about 9.3 ekWh (33.6 million Joules). Diesel contains 10.6 ekWh - a little more - one reason why the fuel economy in litres per 100 km or MPG is a little better than with gas).
A chord of maple (really good burning wood in a stack 4'x4'x8' - that's a lot of chopping if you've never tried) contains about 7,000. ekWh or close to 750 litres of gasoline-equivalent https://www.firewood-for-life.com/firewood-btu.html

However its the transportability and high energy density of carbon-based fuels that have dominated our lives to date and for good reason - the energy density. Consider that 1 litre of gasoline contains the same energy as 33 Mars Bars, or is enough to lift a 1-tonne (1,000 kg or 2,200 lbs) mass over 3 km into the sky......our 5-tonne elephant is therefore over 500 m above our heads.....

That's one reason why electric cars have been slow to adopt - repeating that same energy density is simply very hard to do. (they are more efficient though - at least double).

https://www.engineeringtoolbox.com/energy-content-d_868.html