Dry Wines are the majority.
A wine is dry when the yeast converts all sugar into alcohol.
Examples of dry wines: Chardonnay, Sauvignon Blanc, Pinot Noir, Cabs.
Medium Wines have some residual sugar.
In a medium wine the yeast does not convert all sugar into alcohol.
Most examples of medium wines are white or rosé such Riesling or White Zinfandel (rosé).
Sweet Wines are very high in sugar.
Sweet wines are produced when the yeast stops converting sugar into alcohol.
This happens for 2 reasons: 1) the grapes are extreme high in sugar (late harvest) or 2) the yeast is killed by adding distilled spirit.
Examples of sweet wines are: Sauternes, Ice Wine and Port.