The Distinction
Energy is a total amount — how much work or heat is stored or delivered. Power is a rate — how fast that energy is delivered. A battery stores energy (in watt-hours); a charger delivers power (in watts). The same energy delivered faster means higher power.
The Units
Energy is measured in joules (or watt-hours, calories, BTU). Power is measured in watts (joules per second), kilowatts, or horsepower. Converting energy units (e.g., kWh to joules) is a fixed multiplication; converting power units (e.g., hp to watts) is also fixed — but you never convert energy directly to power without a time factor.
The Linking Formula
Energy = Power × Time. So a 2 kW heater run for 3 hours delivers 6 kWh of energy. Know two of the three and you can find the third.