Flashstaking is simply the combined action of staking principal tokens and burning (FlashBurn) the received fTokens for yield all in one transaction.
The Flashstake protocol exposes a function called flashStake which allows the user to do just this. The user can also specify a slippage value to ensure their transaction cannot be frontrun.
Users can interact with the Flash Protocol and Stake principal tokens into one of the registered Strategies. The strategy determines the number of fTokens to mint and the Flash Protocol mints these to the user’s wallet.
fTokens represent the yield the user is entitled to. You can read more about fTokens here.