The private keys of your accounts, which are required to sign off for any transaction, are on the ZERO and never leave your ZERO. In Rabby Wallet you can see an overview of your accounts and initiate & broadcast transactions. You will always need your ZERO to sign transactions.
You could say that your accounts are all on the blockchain, actually. Similar to the LIQUID app, Rabby Wallet acts as an interface for the online world while ZERO protects your private keys.