I agree with EP....however, let's suppose, just for the sake of argument, that
f(x) = x^2 + 3x - 2 and we want to find f ( x - 3)
So we have (x - 3)^2 + 3(x - 3) - 2 simplify
x^2 - 6x + 9 + 3x - 9 - 2
x^2 - 3x - 2
Look at the graphs, here : https://www.desmos.com/calculator/2fwmyzx9zo
Note that f(x -3) shifts f(x) to the right by 3 units [which we should expect ]