Most decks are supported by 6x6 pressure treated posts. Some decks are supported by steel or concrete piers. The supports will require a positive connection to the footings and beam. This can be achieved by installing a post base connector attached to the footing with an anchor bolt. Another option is to bury the post. Support posts must be rated for ground contact in order to be buried. Post beam connections can use a notched post in order to secure the beam with (2) 1/2" bolts.
Some deck builders wrap support posts with vinyl or composite covers. These covers will either slide over the post or snap together surrounding the post. The purpose of the covers is to conceal the post with a more attractive covering. Deck supports can also be finished with stone, brick or wood to offer a decorative and more massive base to the deck.