We've just created a simple function. Like the car you own, it does not drive by itself. You can supply different data into the function each time. What this means is that you can create one function, and use it over and over again. An example should clear up this.
Lets do an example that calculates the area of a trapezoid.
They are the parameters. Well, in JavaScript, we could, and the result is the combination of the two strings into one. You are not limited to passing actual values into a function that accepts parameters. You can also pass in variables can contain these values. This adds flexibility to your functions.