A wine glass can be broken down into four parts; the base, the stem, the bowl, and the rim.
The base provides stability to the glass, and from the base comes the stem which provides something for the taster to hold on to without affecting the temperature of the wine which resides in the bowl.
The bowl is the most important part of your wine glass. It should be large enough to swirl your wine without any spills or splashes, but it should be tapered to concentrate all the aromas. Red wines typically need more room to breathe, so a larger, wider bowl is ideal. White wines typically need a smaller bowl (they tend to be more U-shaped and taller) to maintain the cooler temperature and enhance aromas. For sparkling wines, flutes are the perfect choice to help preserve your bubbles.
Lastly, you have the wine glass rim, which should ideally be thin and smooth for easy wine flow and drinking.