Manual

Battlegrounds
Battlegrounds are a special type of zone where unique player versus player
challenges can be found. They exist on both PvE and PvP realms, and provide a
level of competitive inter-faction play that can't be found anywhere else.
Battlegrounds are special areas distinguished by a red instance portal. The first time
you encounter a battleground, you must walk through this red portal to enter it,
although later, you can journey there via flying mount if you unlock the flight path
there.
In a battleground, player versus player combat is always enabled, regardless of
realm type. This gives players on the PvE realm who want a taste of PvP gameplay
the ability to do so on more manageable terms.
While in a battlegrounds area, you can team up with friendly players while you
embark on quests designed to pit you against players of the opposing faction.
You can easily leave a battlegrounds area and return to the normal world by
speaking to another friendly battleground NPC.
PvP Messages
You can get an update of player versus player action on a local and global scale
through the Local Defense and World Defense chat channels. By default, these chat
channels are turned off, but you can turn them on by typing "/join localdefense" and
"/join worlddefense" at the chat prompt. You can also turn off these channels by
typing "/leave localdefense" and "/leave worlddefense".
When these channels are turned on, a "zone under attack" message appears in your
chat log any time an opposing player attacks a friendly NPC in the mentioned zone.
This tells you where enemy players are acting so you can confront them if you so
desire.