Creature
Creatures represent warriors, minions, beasts and monsters that serve the player, usually by fighting on his or her behalf. Because almost all creatures can attack each turn to reduce an opponent's life, or block the opponent's attackers, creature cards are fundamental to most deck strategies.
Creatures are played on the player's own main phase, when the stack is empty. When a creature comes into play or changes controllers, it has what is commonly called "summoning sickness" until the beginning of its controllers next turn. A creature with summoning sickness cannot attack or use an activated ability with the tap symbol in its cost, but it can block or use any other abilities it has. A tapped creature cannot attack, block, or become tapped as a cost.
On the bottom-right corner of each creature card is that creature's power and toughness, respectively. The power is the amount of damage a creature deals to an opponent or other creatures in combat, and the toughness is the amount of damage a creature can survive. A creature with damage equal to or greater than its toughness has "lethal damage," and is destroyed. Similarly, a creature whose toughness is reduced to zero or less will go to its owner's graveyard (though it is technically not destroyed.) Any damage a creature takes will accumulate until the end of the turn, when all damage is removed from all creatures.
Unlike other card types, almost all creature cards have a subtype, also referred to as a "creature type." There are no rules inherent to creature types, but there are many cards that affect specific types. In addition, creature types are often associated with particular colors and abilities, typically for flavor purposes. For example, angels are almost always large white flying creatures, spiders are typically green creatures with high toughness and an ability to block flyers, and goblins are often small red creatures with self-destructive abilities.