Halaa is surrounded by four wind rider / gryphon posts which can be destroyed by whichever faction controls Halaa. If you want Tibia coins to wrench control of Halaa from the enemy, you can fix one of the wind rider / gryphon posts by clicking on it, and then use it again to hop onto a wind rider or gryphon. Outdoor pvp has its own currencies and rewards.
Zangarmarsh and Hellfire Peninsula use Marks of Thrallmar / Honor Hold, which can be turned in for different rewards in each zone.
Terrokar uses Spirit Shards, which can be looted from bosses in Auchindoun instances, but only if you have the pvp buff active on you. The rewards can be gotten in Stonebreaker Hold or Allerian Stronghold; you can get a ring, helm with Meta gem slot, and a Meta gem.
Halaa in Nagrand uses Halaa research tokens and Halaa battle tokens. Research tokens can be gotten by turning in Oshu’ gun crystal powder, which can be dropped by all mobs in Nagrand.
Battle tokens can be gained by killing players of the opposing faction near Halaa. Most Halaa rewards require both Research and Battle tokens.