How do players attack other players?

The PvP realm type features Player vs Player play-style. The main difference between a PvP realm and a PvE realm is that in a PvP realm entering any contested or enemy territory automatically flags you for PvP combat and you cannot unflag yourself while in these zones. Cairne is a “Normal” or PvE-Player vs Environment-realm, Laruuna, and you should not become flagged automatically. There are ways that you may become flagged for PvP, as described above, which will allow the other faction to kill you.

If you need further clarification after the posts that have been provided above, please ask. I would be happy to go into further detail.