During the fermentation process, Port is fortified with brandy. This brings the fermentation to a complete standstill and allows some of the grape-sugar to remain in the juice. Although Port is certainly on the sweet side, it is capable of showing extremely intense aromas and complexity.
Most Ports are filtered and there is no need to decant them. As a rule of thumb you can determine whether or not to decant your Port based on whether the wine has a real cork or a cork stopper. If the wine is sealed with a real cork you should probably decant it. Contrary to popular belief, a cork stopper does not equate to a lower quality Port. For example, almost all 40 year old Tawnies are equipped with a stopper but are very high quality and pretty expensive Ports.
A big advantage of a Port with a stopper is its durability; you can leave those open for a week, even up to a month if it is a Tawny Port and you can resist finishing earlier.
All Port is stored in big vats for at least 2 years. Some of these wines are directly bottled from the big vats (Ruby) while other wines are transferred into smaller barrels for further ageing (Tawny).