How dose cover run?

I have a question, if the point of origin of a Fireball spell is on the enemy's side, but the caster is on the other side of cover, do the enemies receive the benefit of cover?

And in the PHB it says: “target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.” But I don't know how to get it.Dose originates means the point of origin or caster?

The spell was cast from the caster's position, but the effect originates where the caster chooses to have the fireball spell activate. So the enemies do not receive the benefit of cover.