ELI5: Watts (capacity?) vs Watt-hours (usage?)

My power bill will say I've used X amount of watt-hours, and I can read that my power plant has a capacity of X MegaWatts, how do the two relate?

Or, on a larger scale, I'd like to have a better understanding when I read things about power that talk about "US power supply: X Gigawatt, Avg. US power consumption: Y Megawatt-hours per year".

Apologies if this has been asked but my search attempts simply found "watts vs volts vs amps" but nothing about "watts vs watt-hours".