How does combat damage work in Magic: The Gathering?

In Magic: The Gathering, combat damage occurs when a creature attacks and is not blocked by another creature. The attacking creature deals damage equal to its power to the defending player or planeswalker. If the attacking creature is blocked, it deals damage to the blocking creature instead. Damage is subtracted from a creature's toughness, and if the damage is equal to or greater than the toughness, the creature is destroyed.