The vault contracts have access to the IST mint, receive a price feed from the Flux Aggregator Contract, and work in tandem to allow a user to lock a collateral asset and mint IST against that asset, subject to several parameter constraints.
Once a Vault is opened, the holder can adjust it by depositing/withdrawing collateral and minting/burning IST in any combination, so long as their resulting vault meets those core parameter constraints. Users may open multiple vaults of the same type if they wish.
When a new collateral type is added to Inter Protocol's Vaults, a new Vault Manager contract is instantiated which provides independent settings for risk parameters specific to that collateral type. In the future, there could be multiple Vault Managers per collateral type which would allow different tradeoffs in risk vs. fees.