Someone is chosen to be the dealer first, and play continues to the left as in most card games. The dealer will deal five cards to each player if there are more than two people playing. If there are just two people playing, each person gets seven cards. Usually just a single deck of fifty-two cards is used. If there are six or more players, it is best to break out another deck of cards.
Once the dealing has been done, the unused cards go face down on the table and the top card is turned face up next to the pile. The upturned card will now start the game. When the players go around in the turns, they will lay their cards on top of that upturned pile.
The reason the game is called Crazy 8's is because the 8's are wild. If the top card turned over is an 8, the dealer can call the suit that needs to be played. Just because the 8 may be a diamond, for example, the player who lays it down can call spades if they so choose.
If the top card turned over is not an 8, then the next player has the choice of playing any card he or she has in the suit presented. They can also choose to play the same number of the card if they do not have a card of the same suit.
For example, let's say the upturned card is a 2 of diamonds. The player can choose to play a diamond of any rank, or a 2 of clubs, spades, or hearts. If they lay down a 2 of hearts, they have changed the suit to be played by the next player. Should they not have a diamond or a 2 to play on the top upturned card; they need to draw cards from the face down pile until they get a diamond, or another 2, in order to play.
Changing suits can also make it more difficult for the next person to play a card. There is a "but" to that statement. There have been times where the next player only has one card and you may change to the one suit they have left to play. If they lay down their last card, they win the game. You may also lay down a card with the exact ranking they have. Strategy is good, but it can also backfire.
The game continues in such a manner until someone has laid down their last card. That player is the winner of the game.
There are some rules that say if the deck to draw from is used up, you can turn the play pile over, keeping the top card and continue with the game. Many people play on when the deck is used up by skipping their turn until there is an upturned card they can play on.
If you want, you can play for points by having the winner get no points for their round, while all others take 1 point per card for every leftover card in their hand. Should you decide to keep score that way, the winner would be the person with the lowest score at the end of the whole game, with individual winners per hand.