@aescling @wallhackio it is played with 40-card spanish decks (1-7 and 10-12 of clubs/swords/cups/gold (bastos/espadas/copas/oro)). (some details of my description will probably differ from when you play with more than two people, in which case it's usually played in teams of pairs; i've only played with just my wife so far).

it consists of a series of 3-card hands until one player reaches 30 points. in each hand, the player who didn't deal (mano/hand) plays first, playing a card, then the other player plays a card, and the better card wins that part and goes first for the next card. if you win 2 of the 3 cards you play in the hand, you win the hand and gain 1 point.

however, when it's your turn to play, you can call "truco" to offer to make the hand worth 2 points. the opponent can then either accept the bet, raise with "retruco", or fold; if they call retruco, then you can accept (bringing the value of the hand up to 3 points), raise again with "vale cuatro", or fold; then that's as far as it goes and they have to either accept (making it worth 4 points, hence "vale cuatro") or fold. if a player folds their opponent gets the current value of the hand (e.g. if you fold in response to a call of truco, your opponent gets 1, but if you accepted and then later folded, they'd get the 2 points; if you call truco and they call retruco and you decline then they get 2 points, etc.). these bets are useful both to try to get more points out of a good hand and of course to bluff the opponent into folding when you've got a terrible hand.

when folding (whether because you're declining a bet or because the opponent has shown enough of their cards to make clear you can't win), it is traditional to conceal the faces of your remaining cards to avoid giving away information.

in addition to truco, during your first play of each hand, you can call "envido" if you have two cards of the same suit (or if you're bluffing). this bet is resolved separately from the main hand (and indeed often winning envido is anticorrelated with winning the hand itself) and is worth two points. your opponent can either accept (as a 2 point bet), raise (several options), or decline (giving you 1 point). if they raised you can then accept, decline (giving them the current pre-raise value of the envido), or raise again (if there are any remaining raises available). raise options include, from lowest to highest, "envido" a second time for +2, "real envido" (+3), or rarely "falta envido" (in which case, the winner of the envido gets points equal to the amount necessary to bring the opponent to their next multiple of 15), and you can only raise with a higher-ranking bet that the preceding one (except that you can respond envido to the initial call of envido). raising in envido adds the value of the call to the value of the bet: envido - envido = 4, envido - real envido = 5, envido - envido - real envido = 7, but falta envido essentially cancels out the other bets and limits it to just the falta envido points.

if some level of envido is ultimately accepted, the person who is the hand (i.e. plays first this hand) declares the envido value of their hand (which is equal to 20 plus the face value of their 2 cards of matching suit with 10-12 being worth zero); the other play either says their amount if it's higher or acknowledge the hand's victory in envido. if the winner of envido does not eventually show their matching cards during the hand they don't get the points. in the event both of the players were bluffing and doesn't actually have two cards of the same suit, their envido value is instead equal to the value of their highest non-face-card (since face cards 10-12 are still worth 0), without adding 20.

the ranking order of the cards means that 5s, 6s, and 7s are good for envido but quite bad for the main hand (except for the 7s of swords and gold, which are the 3rd and 4th strongest cards). it goes 1 espada > 1 basto > 7 espada > 7 oro > all 3s > all 2s > other 1s > 12s > 10s > 11s > other 7s > 6s > 5s > 4s. as you can see, other than the good 7s, all the good cards for truco are worth hardly anything in envido.

some people also play with another bet called "flor" that involves having three cards of the same suit but we haven't played with it so idk how it works.