How come when ppl pour wine into a glass?!

Well, it depends on the glass. And the wine. It started because red wine needs to be poured into a wider rimmed glass to let it breathe. As the red wine reacts with the air it changes taste - which is why you never top off someone's glass if they are drinking red wine because the first sip is so different from the last. This is also why you should never re-cork red wine. With a wider-rimmed glass you can't fill it up quite as high because as I'm sure you know, red wine doesn't come out of any kind of cloth, so you really shouldn't risk a spill.

Part of the appreciation of a good wine is the bouquet. Sniff before you drink. In the case of a "corked" wine, you can realize that you have a problem before you put that swill in your mouth.

It leaves room for air to mix with the wine in the glass and allow the esters to be released. This makes the taste and smell more complex and pleasing.

You are supposed to "sniff" the fragrance and roll it around your palette as some sort of taste survey. It's a snob concept.