If you ordered the wine in a restaurant, you will usually be asked to taste it. Remember, it's not to see if you like it, but just to check it's not corked.
The waiter will show you the bottle and the cork so that you can verify your wine's identity. Never smell the cork; it is there for you to see the information on it.
You will be served a small amount in your glass. Swirl the wine in the glass and give it a sniff. Amateurs or the under-confident should also take a small sip.
If all seems in order, say "that's ﬁne" to the waiter to indicate that you're happy. Once you have given the nod, everyone else will be served.
If the wine is corked, it will smell musty, a bit like an old dishcloth. Bits of cork (or sediment) in the wine are not a reason to send it back and don't mean that it's corked. Remember, a screw top wine cannot be corked.
Don't be intimidated by those self-proclaimed experts who demand to know which flavours you can detect. Smile, pronounce it delicious and avoid the question - at least you haven't fallen into the trap of making a boring exhibition of your ignorance.