Welcome to Subeta! Once you earn some sP, there are also slots that can be purchased in the Millionaire's Centre (Located in Centropolis on the Subeta map)

As mentioned, there are also often events where users can work together to earn more slots as a reward, and for long time account usage, a pet slot is also one of the reward options available :)

Useful Links:

What to do on Subeta? FAQ Useful general information for newbies Finding friends (Chit Chat) SubetaLodge (Offsite item database, pet colours etc.)
Current event: Morostide