If you do not smell a wine or simply take a brief cursory whiff, very little information goes to the brain, and not surprisingly, you have trouble deciding what the wine tastes like.
You want to start by swirling the wine in the glass. Swirling aerates wine. As for actually sniffing the wine, nothing is achieved by holding your nose 2 inches above the glass and taking a polite whiff. You must get your nose (a big one is an asset) into the glass near the liquid. Then take a series of short quick sniffs.
Why not one long inhale? Imagine putting a grilled steak at one end of the room, and tying up a dog at the other. The dog wouldn’t take one long deep breath, but instead, would sniff rapidly and repeatedly, to maximize the impression of the aroma. Since the nose fatigues quickly- in about six seconds- you must try to assess the aromas in the glass immediately. This requires considerable mental focus.
The smell of a wine may be called its nose, aroma, or bouquet. In Britain, smelling a wine is often referred to as “nosing it.”