Adoptable Characters.
While it is more common that new joiners create and play their own characters, some people may decided to "adopt" another member's character that they have made. A reason for this may be a lack of idea/inspiration to make their own character, a desire of wanting to start the game with a new character that has connections or a plot, or just simply because they liked the look of another person's character that was listed as up for adoption. Adopting a character is a great way to play a new character that you could have more muse for, mainly as they typically aren't just a "blank slate" and have some substance/fleshing out done already.
However, you may be asking, why put a character up for adoption? The main reason people add a character up for adoption is because they have an idea they want to share as adopted characters usually come with a plot—for example they could be a sister, father, ex mate of their character. It's important if you do look into adopting a character you are willing to participate in the creator's plot.
NPCs in the Game.
An NPC (Non-Played Character) is when on top of your own character you temporarily play, or control, another character that does not technically exist yet (e.g. is not an active played wolf in RoW). Typically RoW does not allow NPC's in the game, however there are a few circumstances where they can apply. If you wish to join with a character and want to play the character you wish to adopt out as having joined with your own you, if you ask for permission you may be allowed to NPC them for two weeks until they either find a player or you have to stop. Another way NPC characters may exist is when cubs are in the early stages of their lives and don't have players or when pack wolves are on absence.