Step 1 :The vertex of the quadratic function is given by the point \((h, k)\).
Step 2 :The axis of symmetry is a vertical line passing through the vertex, so its equation is \(x = h\).
Step 3 :Since the coefficient of the \(x^2\) term is \(a\), the parabola opens upwards if \(a > 0\) and downwards if \(a < 0\).
Step 4 :If the parabola opens upwards, the minimum value of the function is the \(y\)-coordinate of the vertex, which is \(k\).
Step 5 :If the parabola opens downwards, the maximum value of the function is the \(y\)-coordinate of the vertex, which is \(k\).
Step 6 :So, the minimum or maximum value of the function is \(\boxed{k}\).