Almost everyone has had the horrible experience of trying to open a bottle of wine without a corkscrew. Trying to use a screwdriver and hammer to drive the cork into the bottle results in lots of wine being splashed all over the place and bits of the cork floating in your wine.
What is it? At their most basic, corkscrews consist of a 'worm' (the metal part that screws into the cork) attached to a short bar across the top. While this old-fashioned type is still available, it's extremely difficult to use because there's nothing to help lever the cork out of the bottle; you end up putting the bottle between your legs (very undignified) and using brute strength to pull out the cork.
What to look for: It's important that the worm is long enough to go deep into the cork. If it's a short worm, you might pull out only part of the cork. A foil cutter is also useful.
Types: There are three main varieties of modern corkscrews. One type doesn't have a worm that screws into the bottle; instead, you pull out the cork by slipping two thin pieces of metal between the lip of the bottle and the cork. This is difficult, requires strength and often results in the cork breaking in half or being pushed into the bottle.
A second variety has the metal worm and an 'arm' that hooks over the lip and neck of the bottle and is used to lever the cork from its home. It takes practice to get the worm to go straight down the centre of the cork, but if you manage to do this, it works well. It's also sleek and compact, and usually comes with a built-in foil cutter.
The easiest type of corkscrew to use lets you twist the worm in one direction, which screws down into the cork and then - like magic - lifts it from the bottle. The worm is in a frame that fits securely on the lip/neck of the bottle so it goes straight down through the centre of the cork. It also comes with a foil cutter. Screwpull is the best-known maker of this type of corkscrew and it makes several versions ranging from the basic one just described to fancy (and expensive) lever models that drive the worm into the cork and pull it up in two quick motions.