Surely, you heard of the terms kW (kilo watt) and kWh (kilo watt hours). To understand solar energy and to correctly size a solar system that meets your needs, you will need to understand the difference between Power and Energy.
Watt ‘(W) is a unit of Power. 1000 Watts is one kilo watt (kW).
Watt hour (Wh) is a unit of Energy. 1000 Watt hours is one kilo watt hour (kWh).
The easiest way to explain the difference between Power and Energy is with a running analogy. Power is how fast you can run. Energy is how long you can run.
Check out this previous post titled The Amazing Math of Solar Energy. It has a good explanation for Power and Energy in the context of solar energy.