Index -> Interface -> Tournaments Lobby -> Types of Tournaments
There are two major types of tournaments: Constructed and Sealed. All tournament styles have timed games, using the same "chess clock" you can choose to play with in a casual game.
Constructed tournaments require you to bring a deck to the tournament, composed of cards in your collection.
Sealed tournaments are a Limited format. These tournaments require you to bring unopened boosters and/or starters, and players compete with decks made from the cards they open. Your general collection is not used in a Limited tournament (though cards you use in a Limited tournament join your general collection at the conclusion of the tournament). Limited tournaments have a Deck Building phase before the first round where players use the Limited Deck Builder to create their tournament decks.