There are several steps to do so......
1st>>>> Employ the four basic criteria used to differentiate wines. These are smell, color, clarity and,of course, taste. As a beginner, don't get too caught up in the incredible subtleties and variations in wines or you may become overwhelmed by the complexities involved.
2nd>>>> Open your bottle of red wine and let it sit for a while. Allowing the wine to "breath" like this is essential. You are introducing oxygen to the wine and bringing out its full flavor, which will help you differentiate one red wine from another.
3rd>>>> Swirl your wine, check its clarity against a white background, inhale its "bouquet" and taste it. These basic tests will then allow you to differentiate one red wine from another. The differences between one red wine and another include the type of grape or grapes used to produce them, the climates where they're grown and the ways they are aged. These factors result in variations that produce the different types of wines, such as Merlot, Cabernet and chianti.
4th>>>> Drink red wine from a glass with a short stem and large reservoir. The thought here is that the heat from your hand will react with the wine and further bring out its natural flavors.
5th>>>> Notice a subtle taste of tea along with a full-bodied flavor of berries when you are sipping a Cabernet. On the other hand, if your wine has a fruitier taste, then the odds are good you've got a Merlot.
6th>>>> Learn to drink like a pro before you can differentiate wine like a pro. Do not simply gulp down that glass of red wine. There are rules to follow and an etiquette to maintain. Smell the wine, take small sips and get a visual impression of the color of the wine you're drinking.