Suppose that the early universe was filled with energy uniformly. Would quantum fluctuations cause variations in energy density across space resulting in regions with higher and lower energy density than the mean?

I don’t really understand how quantum fluctuations work so I may have got it all wrong.

Suppose that the early universe was filled with energy uniformly. Would quantum fluctuations cause variations in energy density across space resulting in regions with higher and lower energy density around the mean?

I read about quantum fluctuations online and still don’t understand how it works so I may have got it all wrong.