The vertex is the highest or lowest point on a graph, also known as the maximum/minimum. It is the turning point for the parabola.
In this case, it has a maximum, because the parabola points downward.
Using the graph, we can see the vertex is at point
The vertex is a point that is the maximum or minimum of the parabola. (3,4) is the highest point on that parabola so it's a vertex