HAIR COLOR question: Developer or activating lotion?

Hey, I'm going to do a brave/stupid thing and color over my recently faded highlights (which have faded from a rich burgundy in my black hair to a bry orange--yeesh). I bought Wella Color Charm Demi-Permanent Hair Color in fiery red and I know I have to mix two parts developer, one part color. But I just looked in their "guidebook" and it says to use two parts "activating lotion"?? They have a separate developer (10 volume, 20 volume, etc) and a separate "activating lotion." In the guidebook directions they only mention using 2 parts of the lotion and one part color, none of the developer; but everywhere else I look for directions, it says to use DEVELOPER (10-or 20-volume) to mix with the hair color. Which should I mix with the hair color, the activating lotion, the developer, or both? Or does it not matter? Is Wella Color Charm the only "activating lotion" out there (I don't think that would be the case, like it's a special product of Wella's, but then what's the developer for?)