The turning point is known as the vertex when we talk about parabolas. The vertex is either the highest point or the lowest point. In this case, it is the lowest point.
The graph shows the turning point at (-2, -1)
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The term "root" is another term for "x intercept". This is where the graph crosses or touches the x axis.
The two roots are (-3, 0) and (-1, 0)
Since the y coordinate of any x intercept is always y = 0, we can state "the roots are -3 and -1" to indicate what is in bold above, just in a shortened way.
Side note: the x coordinate of the vertex is always halfway between the x coordinates of both roots of any parabola. The vertical axis of symmetry passes through the vertex.