Challenge

Challenge Rating (CR) summarizes the threat a monster poses to a group of four player characters. Compare a monster's CR to the characters' level. If the CR is higher, the monster is likely a danger. If the CR is lower, the monster likely poses little threat. But circumstances and the number of player characters can significantly alter how threatening a monster is in actual play. The Game Master's Guide provides guidance to the GM on using CR while planning potential combat encounters.
Experience Points
As they overcome challenges and complete adventures, characters earn Experience Points (XP), which are awarded by the Game Master. When a character's XP total crosses certain thresholds, the character's level increases. The Game Master's Guide provides guidance on awarding XP.