What is the Return statement used for?

Formally, the definition of the return keyword is "a statement that tells the program to leave the subroutine and return to the return address". Essentially, if we wish to return a result from a computation or various other scenarios that are concluded from a function, we use this keyword to do so. See this example of it's potential applications:

local numberA = 5
local numberB = 2

local function multiplyNumbers(a,b)
    return a * b
end

local result = multiplyNumbers(numberA, numberB)

This will return the multiplication of parameters A and B to wherever this function—or the fancy term "subroutine"—was called, as aforementioned above. To break this down, this is what's occurring:

local result = a * b
local result = 10

An easy way to grasp return, is to see is as the "give back" keyword. Before I finish, let's see another example:

local hello, world = "Hello", "world!"

local function concatenateStrings(a,b)
    return tostring(a..' '..b)
end

print(concatenateStrings(hello, world)) --> 'Hello world!'