When you first move over to the FTM chain you will no longer use ETH, BNB etc for gas fees. You will now be required to use FTM. That said, when you make your first swap of your native tokens you are bridging you will need to pay the gas fee for that transaction in FTM, which of course, you won't have as of yet. Fantom strives to be a very welcoming chain and entire community the the faucet system is just another example of how we all strive towards such!