Q. How can I register my friends?
A. You can send friend request to suggested friends from the Community > Friend menu.
And you also can be a friend with other White-Wulves with friends searching feature.
In addition, If you become a friend with other White-Wulves, you can hire their heroes at Raid/WorldBoss battle with lower cost.
If you hire friend's hero as mercenary 3 times, you can get the energy as reward from the friends list.