From one of the PK videos posted in another thread, forced PvP is similar to what I've seen in other games where when you force PK someone, you get the rewards of part of their loot. The downside however is that your name changes different colors based off the offense.
In the video posted, the player PK'd a bot and their named turned red.
1. Safety Zone = towns/hubs. Safely deposit loot, AFK in peace, etc.
2. Common Areas = you can force PK someone and take part of their loot, but there is not enough information posted to know whether it's just loot, or if it's equipment as well. We also don't know the drawbacks of the "red name". In one of the other games I played with a similar fashion, if you force PK too much, your name would upgrade to black and on death you lose everything in your bag and equipment. I definitely foresee something similar in place.
3. Conflict Areas = Gankfest is right. STV for those who played WoW. No Force PK downside means fire at will. But expect retaliation if you PK the wrong person.
4. Siege is like a town battle. More information here: