Describe the differences between a parabola that has a horizontal directrix and a parabola that has a vertical directrix.

 A parabola that has a horizontal directrix is a parabola that opens up or down. 

Here are some of its components: 
1) Standard equation of a parabola with a horizontal directrix: (x-h)^2 = 4a(y-k), 
a = distance from vertex to focus 
2) Vertex at (h,k) 
3) Focus(h,k+a) 
4) Directrix: y = k-a 
5) Axis of symmetry: x = h 

A parabola that has a vertical directrix opens to the right or left and is on its side. 

Here are some components 
1) Standard equation of a parabola with a vertical directrix: (y-k)^2 = 4a(x-h) 
2) vertex (h,k) 
3) focus (h+a,k) 
4) directrix: x = h-a 
5) Axis of symmetry: y = k

Hopes this helps :)