Here is a quick primer. Ruby port is the youngest and least expensive. It is aged in wood for two years and, when bottled, is ready to drink. It does not age in the bottle. It is young and fruity.
Vintage port is made from the best grapes from a single year.
If the grapes are not up to standards, vintages might be skipped. Its flavors are mature, lush and full of character. Tawny port spends its life in wood while vintage port spends its life in the bottle. And it adopts a tawny color. The age on the bottle actually represents an average age of the wines from which they were blended.