Firstly, is the hopper facing into the container that you want it to be flowing into? Did you shift-click(place) the hopper onto the container? I don't think they're disabled :/
You are able to add or remove items from hoppers by directly putting them in or taking them out. Hoppers are unable to suck new items in or push items out into chests or other containers. For now, they function as 5 slot chests.