The directrix and the focus are both parts of the parabola that are the exact same distance form the vertex ot he parabola, the only difference is that they are in opposite directions, the focus of the parabola is always found inside of the parabola and in the axis of symmetry, on the same axis of symmetry both on the outside of the parabola, the same distance from the vertex than the focus you can find the directrix, which is a straight line that is perpendicular to the axis of symmetry.
