Write the equation for a parabola with a focus at  (0,-5)(0,−5)left parenthesis, 0, comma, minus, 5, right parenthesis  and a directrix at  y=-3

Now, notice, the focus point is at 0, -5, down below the x-axis, whilst the directrix is above it, meaning is a vertical parabola, and is opening downwards.  That means the squared variable is the "x".

now, keeping in mind that, the vertex is half-way between these two fellows, from y = -5 and y = -3, there are 2 units, and the vertex is half-way there.  Check the picture below.

now, notice the "p" distance from the vertex to either fellow, is 1 unit, however, because the parabola is opening downwards, is negative 1.