And related: how is the shop organized (if it is)?

You can spend them in the shop, or in rare special auction events that admins organize. 

Click the shop and you'll see how its divided in subsections. 

Edited May 6, 20215 yr by Jubaris

for spending a lot of credits in the shop (200+) you get a top spender token, and thats what you can use in special auctions, not the credits directly.

Otherwise credits can be spend in the shop or if you get credit codes, you can use them for rewarding other players or paying them for services (such as drawings, avatars, etc)