What a function rule?

Answer 1

As you get to harder and higher analysis of functions, it's not required.

A function rule, apparently, is an equation that represents a function.

A function, properly defined, is its graph. A graph is a subset of a plane, where it's the set of all points (a, b), and for every value a, f(a) = b is the definition of a function.

So you can get a plane, squible some lines that's not over lapping, you get a function. How the HELL do you get an equation for that? Hence, the function is kinda useless?

No! Function equations can help us making analysis of those that does have one. In terms of derivatives, limits etc.