In order to use the Solana network you pay fees when you make transactions. These fees are for storage on the Solana network and do not go to Nina. The fee for purchasing a Release is 0.002 SOL which is ~$0.04.
You will also pay fees when you make a Release or setup a Hub. These fees are for space on the network - think of it like storage costs on a cloud service except it is a one-time and ensures that your data is stored.
You do not have to pay fees when following accounts or Hubs, verifying your social accounts, redeeming Release Codes, or collecting free Releases. Nina covers these fees for you.
When you pay a fee Nina does not receive any of the fees, they go directly to storing your data, recording your purchase, etc.