A composition function is one function that depends on another function. To find the value of this composite function we need to substitute one function into the second one.
In other words, you have to apply the function to the first variable and then apply the second function to the result you obtained after the first step.
In this problem you have f(x) = x² and g(x) = x - 3 and you need to find the composite function f(g(x))
First we need to apply the function g (x) = x - 3
Once we've done this, we're going to "plug" this result into the function f(x)
f(g(x)) = f (x-3)
But we know that the function f(x) elevates the variable to its square, therefore f (x-3) = (x-3)²
