Sweet wines are often popular with the beginning of the meal as an introduction to dinner or sometimes served as a dessert wine at the end of a meal.  Not to be confused with fruity, sweet is defined as the amount of residual sugar in the wine. 
Some of the more popular sweet red wines fall into the dessert wine category.  Some of the clues to finding a sweet wine can be indicated on the label.  The process of fermentation is when you take the natural sugars in a grape and convert that into alcohol through the introduction of yeast. To determine the sweetness of a wine just look at the label and at the alcohol content and in most cases, the lower the alcohol the sweeter the wine.  Some of these wines will range between 8-12% alcohols by volume.  There are other wines that are considered sweet that fall under the fortified classification. 
Fortification is where brandy is added to a wine to give the wine a higher alcohol content, which makes the fermentation process stop before all the sugar is converted. The wine is sweeter.  There are many different types of sweet wines to choose from that are great at the end of a meal.