This is a lore-based question! These questions have in-depth answers linked in the image used to ask the question alongside the simple text answer ^^
Pookies are small robotic creatures no bigger than a Shiba Inu. They're made to help their users learn to play video games! Codies are a more accessible digital version of a Pookie. Both seem to share an appearance that looks between a cat and a ferret.
All Main-Adopt Codies are free. Raffles, Breedings, and Customs cost Bytes (species currency) and Bartering using C$ or Pets is the easiest method to get Bytes. You HAVE to have a Colony Archive in order to participate though.