Seria's Room in Elvenguard is your starting location when you log-in to the game.
It has your Safe, Mailbox, Avatar Closet and Seria's shop.
Move to the right gate of Seria's Room to exit to Elvenguard.
Move to the bottom of Seria's Room and you will be taken to the last location you visited.
To move to the Seria's Room of another area, you have to find the portal with a green vine.
It is used for storing items. You can add more slots using expansion/upgrade tickets.
"It also has an account safe. Account safe can be used at Lv. 60+ and it is used to move account-bound items to characters on your account."
This is a convenience feature for changing/storing your avatars.
You can own up to 4 avatar slots.
Items can be sent to your own characters or other players using the mailbox.