The trophies does not give any gameplay advantages but is only there for visual customization and bragging rights. The idea of trophies are like medals, if a enemy character has lots of awesome trophies, that character is probably going to destroy you quickly. The amount of trophy slots will increase with the characters level, a maximum of five trophies can be worn at one time, but all available trophies can be obtained and owned. The trophies' possible placements are more than the actual trophies that can be worn, the trophies can be moved around on the armour without switching slots in the equipment window.
In addition, Trophies obtained for certain tasks will evolve or level up as higher "ranks" of the task are achieved. For example, if Trophy obtained for killing 50 Chaos players is a dagger, that same dagger may become gem encrusted and gold trimmed for killing 500 Chaos and so on and so forth.
Trophies can also be placed on mounts and guild banners.
The majority of the trophies will be unlocked through the Tome of Knowledge. For example - when you have killed a certain amount of enemies in PvE. When the trophy has been unlocked in the Tome of Knowledge the player will get instructions to go to a certain NPC who will hand over the trophy.