Explain how to find the coordinates of the focus of a parabola with vertex (0,0) and the directrix y=5

Keep in mind that, the directrix is "p" distance units away from the vertex, and the focus point is also "p" distance  units from the vertex but in the opposite direction, so in short the vertex is half-way between both of them.

in this case the vertex is at the origin, and the directrix 5 units above it, so that means the parabola is vertical and opening downwards, like the one in the picture below, and the focus point is 5 units the other way.