You need to remove the cork in order to open a bottle of wine, done best by using a corkscrew. A corkscrew extracts the cork neatly, while a bad one will shred the fragile cork bark, leaving pieces in the wine, or worse - shove the cork into the bottle. To remove the cork from a wine bottle there are four key steps:
The foil covers the cork and protects it during storage, shipping, and handling as well serving a decorative purpose. Some corkscrews have a knife to cut into the foil, and there are specialized foil cutters available today, or you can use the tip of the screw as a sharpened point. Some older corkscrews have a brush to remove any debris from the top of the cork, though modern wine bottling uses chemical disinfectants to prevent fungal growth on the cork.
A corkscrew's worm needs to be 4-5 cm long for optimal grip through the length of the cork. It is typically helical with rounded (not sharpened) edges so as to drip but not slice the cork. The tip of the screw is in the path of the helix to minimize damage to the cork. Corkscrews with centre points may cause damage to the cork, since succeeding turns of the helix must expand the hole in the cork. Some modern corkscrews have overcome this issue by clever industrial design.
Because a cork is compressed to help seal the neck of the bottle, and provides an airtight lock on the liquid and gas inside the bottle. Extracting it requires about 100 lbs (45 kg) of force. They try to simplify this task by either using leverage (either a simple or compound lever), torque(using a turning handle like wrench), pressure (pumping air into the bottle), or prongs (a 2 pronged device that is not really a "corkscrew", but grips the cork while reducing friction with the bottle neck).
Because most corkscrews grip the cork while you twist, once the cork is out of the bottle you just un-twist the cork from the screw.