Sealed is about scraping together the best deck from limited resources. You must make do with not the most powerful cards but know that your enemies are also constrained.
In Sealed Tournaments each player is given 5 packs from which to build their army. Each player will end up with different cards. You then have a little while to build an army from these cards. Your army must be at least 25 cards and can contain any cards that you got in your packs. Once each player has submitted their army the play proceeds like a Constructed Deck tournament.
Again these can be either single or double elimination.
The prize payout is the same as Constructed Deck.