Think of it this way to grasp the concepts. By calling a function you are asking it to do something. add(4,3) is a request to a function called add that calculates the sum of the two numbers it is given. In this case, 3 and 4. A return value is how the function communicates the result of what it has done; in this case added 3 and 4 to make 7. So the function returns 7. You can even think of add(3,4) as having the value 7 (in this case, because 7 is what is substituted for the function call).