You can put this solution on YOUR website!
Say that you have an equation y = 3 + x. In this case, the value of y depends on the value of x. In this case y is always 3 more than x.
That same equation can be written in function notation as f(x) = 3 + x. Nothing much has changed here, because in reality, the y really is equal to the f(x). The THINKING, though, is a bit different. The way that you would think in function notation is "OK. I've got a type of machine here. It's called f, and it takes in (inputs) one type of value at a time. It's supposed to do something with my input. In this case, it increases my input by 3". Function notation is a way of writing equations that tell you what variable or variables can be inputted to it.
An important use of functions is in graphing equations. If you've got more than one equation's line or curve, it's convenient to label them f(x), g(x), etc. so that you'll know which line/curve belongs to which equation. That's way better than calling all of them "y=".
BTW, When you see f(x) =, it does NOT mean "f times x equals".