This might be a silly question, but what is the difference between cake flour and all purpose flour? Does it change the quality of the cake?

Quality, no. Texture, yes.
Cake flour has significantly less protein than all purpose flour. Less protein means less gluten formation in the mixing process. Gluten is what gives baked goods their structure. Less gluten means a finer, delicate crumb texture, which is what you want for light cakes like sponge.
For a dense cake like pound cake, all purpose flour is appropriate.
Hope that helps!