Helium is one of the elements that most people see (well, not see since it is a colorless gas) in everyday life. We are familiar with it because it used to fill toy balloons so that they rise in air. We shall get around to the calculation about that later.
Helium also is used for large balloons, blimps, and dirigibles for the same reason: it is lighter than air and so provides lift (not aerodynamic lift, which is provided by air passing over a wing surface) and so causes objects to rise, but these large craft have a payload where toy balloons do not, at least in most cases.
We also know it as the gas that causes voices to take on a bizarre, high pitch. We shall also discuss the reasons for that. But for me at least, helium is of extreme interest because of its quantum mechanical properties.