Fantom is a fast, high-throughput open-source smart contract platform for digital assets and dApps. On Finn Exchange USDT is only used for trade processing. All funds are stored on Fantom as before.
Do you need to purchase FTM to use Finn Exchange?
No. You do not need to do anything, USDT is integrated as part of the stack and is not affecting the user in any way. You simply deposit to Finn Exchange as before on Fantom network or any other supported network.
How does the Fantom contract communicate with the USDT contracts?
Fantom contracts are connected to the USDT contracts through a decentralized bridge that relays messages between the two chains.
More information on the Fantom Chain can be found here