What is the purpose of this append command!

[Captain_farrell]

def square(x):
    return x * x


def my_calculation(x, y):
    result = []
    for i in y:
        result.append(x(i))
    return result


squares = my_calculation(square, [1, 2, 3, 4, 5])

print(squares)

sorry everyone, i am a beginner! in these codes i did not understand why we have to do ? "result.append(x(i))

or if anyone can explain me all steps, would be much appreciated.
thanks again.