For Sealed each player starts by selecting three booster (foil-wrapped) packs.
The players are then paired up, and each member of the pair is given one starter deck at random (the other person gets the second starter deck). Both players then open their starter and all three booster packs.
At this point, the members of a pair can trade cards with each other.
Following the trading period, each player builds his own T1 deck out of the cards available. I believe the only difference in Sealed deck building rules (compared to standard T1) is that you are limited to one (single-color?!?) site per deck.
You then proceed to play the tournament with your shiny new deck.
