A turning point is a point at which the derivative changes sign from positive to negative or vice versa. Then, a turning point coincides with a relative maximum or a relative minimum (also known as local minimum and maximum).
From the table, we see that f(x) decreases from x = -6 to x = 0 and it increases from x = 0 to x = 6. Therefore, there is a minimum at (0, -2)
