Here is a very basic example of a function:
f(x) = x – 3
In this example, for each value of the variable, “x", we will have different value of f(x): when x is 3, f(x) is 3-3 = 0; for x=10, f(x) = 7 etc.
Of course, the relation between x and f(x) can be more complicated, such as
f(x) = 2x + 5, f(x) = 10-0.5x, or f(x) = -5x + 2.5.
Note that in all the above examples there is only one variable, x, and it always has the exponent of one. Those are linear functions of one variable, which has a general form of f(x) = ax+b; when “a" and “b" are constants which determine the shape of the graph. Wait, what graph? We have not mentioned graphs yet, haven't we?