You've looked at the wine, you've smelt it, and at last you get to actually taste it.
The aim here, apart from the pure enjoyment, is to see which of the aromas you identified while smelling your wine you can taste as well. But you're also tasting for other characteristics: acidity, tannins, and sweetness that make up the wine's structure.
How to taste
Here's the bit that beginner wine tasters feel the most self-conscious about when doing it around others - the taste. Suck some wine into your mouth, purse your lips and draw air in sharply - making the signature slurping sound - then close your lips and swirl the wine around your mouth - across your tongue and over your gums. What do you taste and feel?
Most wines are actually dry, so this may be a question of how dry is it. If you are tasting sweetness - ask yourself if this is a fruit taste which is conferring a sweet taste (but can still be dry) rather than a sweet wine. For example - a dry red might have sweet blackcurrant flavours. Think back to the aromas your picked up on smelling to see if this helps.
The way to test acidity is to swallow your mouthful of wine, and immediately lean your head forward 45 degrees with your mouth open. The time it takes for your mouth to fill with saliva is an indicator of how acid the wine is. A couple of seconds suggests an acidic wine, nearer ten seconds is a lower acidity wine. Look out for 'flabby' wines which are very low acidity wines which means the wine will lack structure and be poorly balanced.
When you swirl the wine round your mouth, how does it feel? The feel of the wine is the body - if it feels watery or like skimmed milk, it is light-bodied; if like whole milk, then it is full bodied.
Red wines: tannins
Tasting tannins comes from your gums. They often give astringency to the wine, and can be felt on your gums, in particular above your top front teeth. If your gums feel like paper straight away, then the wine has high astringency and tannins. Tannins can also be felt here but in a smoother way, but you'll feel it on your gums.
This is a continuation of the aromas you smelt from the glass, though some will be more pronounced and others less so.
The finish refers to how long the taste lingers strongly in your mouth. If only a couple of seconds, this is a short finish. Ten seconds is a long finish. Many aged and more expensive wines will have very long finishes, and that is regarded as a mark of quality.