What is the foil thing covering the top of the wine bottle? That's the capsule. Before you can take the cork out of a bottle of wine, you have to get through the capsule covering that wineries place over the tops of their wine bottles. Traditionally the capsules have been metallic, but it's now common to use cellophane and other materials as well. Capsules serve two purposes, one practical and one aesthetic: they keep the corks clean and they look better than bare cork.
Before You Remove the Capsule
The first thing to do before you remove the capsule from the wine bottle is take a look at it to ensure that it is intact. There's little chance of there being a problem, but if the capsule is cut in any way it's a bit like the safety seal on food being broken: whatever is inside is now suspect. The worst case scenario is by far the least likely, namely that the wine inside has been replaced with something cheaper.
A bit more likely is that the capsule was damaged accidentally but this might have allowed something to happen to the cork. So if the capsule has been damaged in any fashion, you will need to proceed with caution from here on out: examine the cork carefully, examine the wine carefully, and take your first sip of the wine carefully.
Removing the Capsule
When opening wine, you should make sure that you remove the entire capsule from the top of the wine bottle. This is important because you want to ensure that none of the wine you pour ever goes over the capsule material — not just to preserve the taste of the wine, but also to keep the situation from getting any messier than necessary.
It's not recommended to use the special foil cutters sold in wine stores because these don't cut the capsule low enough. If you really don't want to remove the entire capsule, you should at least cut about an inch below the rim of the bottle. Many corkscrews — and all Waiter's Corkscrews — come with a small knife attached which you can use to start cutting away the capsule. You can also use this knife to remove the plastic plug which is sometimes placed above the cork.
After You Remove the Capsule
Once the capsule is gone, it's a good idea to use a damp cloth to clean the top of the wine bottle. Remember, wine bottles are typically handled by the narrow top end so who knows how many hands and fingers have been all over it. Even if wine flavors weren't delicate enough to be affected by such contamination, it's just good hygiene to wipe off your wine bottle.
Now is the time to take note of whether any mold has developed on the top of the cork; if so, carefully wipe that away as well. You probably don't need to worry about a little mold on the outside because that may a sign that the wine was stored in appropriately humid conditions. Mold will contaminate wine, however, so you need to get the mold away from the bottle lest the outside mold come into contact with the wine inside the bottle.
If by any chance you discover mold on the inside of the cork when you remove it, that's a much more serious problem and it's likely that the wine itself is already contaminated. Pour some wine and smell it carefully — if it smells bad, the wine has gone bad and shouldn't be drunk. If you can still return the wine to the wine merchant, do so.
If the wine doesn't smell bad, you can risk a careful sip to check it. Most likely you will find that the wine tastes bad because it has spoiled.