A corker is a device used to insert a cork into a bottle, such as a wine bottle. Usually they consist of a tapered funnel, and a plunger which pushes the cork into the bottle. A cheap corker will be usually made of plastic, and the operator has to align the funnel over the neck of the bottle while pushing down hard on the plunger. Better corkers use a dual lever system that provides extra leverage to force the cork down the funnel. Better corkers also have a mechanism to locate and hold the funnel in place over the neck of the bottle. If you plan to do some winemaking, you will need to get one. A cheap corker is okay if you plan to make only a few bottles of wine, but if you plan to make more than a few gallons, then I would suggest investing in one of the better ones.