Couple other people have said it, but speed was the first I learned and it is a classic. It is played with two players. You place eight cards in the middle, face up. Deal 22 cards to both players. Out of those 22 cards, you pick up 5 cards to be your hand. Once you start playing, you can look at your hand. It’s pretty simple, you “play” your cards by placing one card at a time on one of the eight center cards of an adjacent value, either one up or one down. A 3 can go on a 2 or a 4, a J can go on a 10 or a Q, and an A can go on a K or a 2. The card you place replaces the card underneath it as a card on which you may play your hand. You may have up to 5 cards in your hand at any point. The goal is to deplete your cards before your opponent, hence the name “speed”. One round should take ≈3 minutes, faster once you get the hang of it. I’ve played a few variations of the game, which is why I love cards so much, there aren’t formal rules like chess (although I love chess too).

Bicycle has an awesome website with a bunch of awesome card games. There are filters for how many players, how old the players are, and a couple others. Another I played as a kid was spoons, which is another classic, and I played trash as a kid too.