Wine glasses are fancy items that can be placed on most solid surfaces. This is one of the items which can hold many different kinds of drinks. To fill them, right click on a barrel of the drink that you want to fill the wineglass with, and then either place it down on a solid block, or drink it by holding down right click.
Right clicking on a placed wineglass will make you drink it instantly. Also, you can right-click an empty vessel with a full one in your hand, or vice versa to transport the fluids to and from each other.
One way to obtain wineglasses is by looting. They are often found in Dorwinion (most often in breweries). They are also frequently found in Gondor structures (mostly taverns) and in Lindon structures (especially in halls).
Wine glasses can be sold to Dorwinion Merchants. As a result, one profitable technique is to smelt an entire stack of sand into glass, craft it into Wine Glasses and then sell them all to the Dorwinion Merchant for coins.