PvP-only characters (player versus player) are one of two types of characters that can be created in Guild Wars. Unlike roleplaying characters, PvP-only characters cannot enter PvE missions, explorable areas, or outposts outside of the Battle Isles; instead, they begin at the highest level and can compete in any PvP missions and arenas.
PvP-only characters are created with a primary profession, a customized appearance (face, hair style, height, color scheme), and name. They begin at level 20. Once created, the character starts in the Great Temple of Balthazar.
PvP-only characters lose and gain something compared with roleplaying characters. They are fitted to specialize in PvP, and thus cannot play in any PvE area. However, they do not need to buy equipment, level up, charm pets, do attribute quests, or earn skills. Instead they can use any of those things which is already unlocked on their account, whether those skills were unlocked through PvE play (on another character), through PvP faction-based rewards, or by purchasing the PvP Unlock Pack. PvP characters also have exclusive access to the PvP Equipment panel, which allows them to save and load configurations of armor, weapons, runes, and other customized parts of their build. Even a PvE character that reaches level 20 and buys all the same preparations will not get this extra efficiency.
To enjoy the entire game, it's worthwhile trying both a PvE and a PvP character. Since every copy of the game comes with multiple character slots, you can have both at the same time.