Everyone is at a Mascarade trying to use their powers to become wealthier than the others. Every character has special abilities to use on their turn. In some games you would have to be that character in order to use those abilities. But in Mascarade you can bluff about what character you are playing as sometimes you might not even know what character you are!
There are three actions players can take on their turn. They can use one of the powers available in the game (not all characters are used each game) and then all of the players in order decide whether they want to claim that power as well. If no one else claims that power you use the power without revealing your character. If other player(s) claim they are also that role then everyone flips over their card and anyone who is that character uses the power and then everyone who lied pays a fine to the court.
Instead a player can trade or pretend to trade character cards with another player. By doing the trade under the table you are the only one who knows if you switched cards with the other player or kept your original card. Sometimes we get too absorbed in being sneaky that we forget whether we switched cards or not!
The last thing you can do on your turn is just look at the card you currently control. While this can be informative it is likely to cause players to trade with you before your next turn removing any advantage you had by knowing your character.
Mascarade is a fun game of trying to figure out what role you have or faking it until you can get the 10 coins needed to win the game. Lots of similar games require you to be able to lie or bluff convincingly,but this one can be won with just good manipulation of the characters! If you have a group of friends and are looking for a quick deduction game you can win without being deceptive this is a game to try!