can sombody explain what a return is in functions?

Hello I'm learning about functions, but the return in functions makes no since to me can somebody explain for a beginner ?

myVariable = 5

function hello() print("hi") return"100" end

print(myVariable)

myVariable = ("hello")

Im just not seeing what the point is of the return or what its use is or value. I see people using returns in functions often, but I never use them in my functions can somebody explain?