A function is anything you put as an Input x and gives you a different output Y.
Suppose you get 5 candy bars for 1 dollar...
This means for every x1.00 dollar you for y5 candy bars.
so if you had 2 dollars you get 10 and so on...
Now what is not a function is two Xs with a different Y.
so say you use the same dollar to buy 5 candy bars then, with a dollar again you buy 3 candy bars.
This is not a function because you gave the same amount of money and go a different out come of Y. So this let's you know you got ripped off.