To determine which values of x we would use for creating a graph of a parabola, we need to know where the line of symmetry, or the axis of symmetry is. For that we can use the equation:
y=(x-h)+k, where we know h and k.
From this equation we can see that the line of symmetry is passing trough x=h.
And now we can determine which values do we need to add to h and to subtract from h to get values of x to create the table of values to plot a parabola.