The object of the game is to get rid of your hand as quickly as possible, and card combinations help you do that since you can put down more than one card at a time.
So, depending on the rules, it is okay to look at other player’s card or play out of turn if you can get away with it. Note this is also how the game derives its name. A king of clubs beats an 8 of hearts because even though the hearts suit is higher than the clubs, the king is higher than an 8. For instance, the 9 of spades is higher than the 8 of hearts.
This also runs the works across all the suits. For instance, a 2 of hearts beats a 2 of diamonds.
In this version, the rules are as follows: A lot of people play with slightly different rules in different geographical areas or cultures, and it's best to be clear about what you can and cannot do before the game begins to avoid confusion or frustration during the game.