Can someone explain Return to me?

Return is applicable in many ways. You can get values on a long formula, but you only have to type in the formula once. For example:

Instead of

x = math.sqrt(math.pow(3 ,2) + math.pow(4 ,2))
y = math.sqrt(math.pow(6 ,2) + math.pow(12 ,2))

print(x)
print(y)

You can simplify that into one function:

x = 3
y = 4

p = 6
q = 12

function PT(a, b)   -- Pythagorean Theorem
    Answer = math.sqrt(math.pow(a, 2) + math.pow(b, 2))
    return Answer
end

print(PT(x,y))
print(PT(p,q))

Of course, there are other useful things to do with return, but this is just one example.

The gist is that you're literally converting a function into a value.

Take note that a return statement immediately stops the function, so anything besides ends after it will error out.