Question

What is the equation of a parabola with a vertex at (-2, 0) and a directrix x = -4.

Answer 1

do you have a sideways parabola or a non-sideways parabola?
which equation for a parabola do you think we are using?

Answer 2

this is really helpful:
p is the distance between the directrix and the vertex (or the focus and the directrix)
but to determine the sign of p, you need to know which way it opens up