BitFinex offers three main functions - it is a pure bitcoin to fiat exchange, a margin trading exchange and a liquidity provider.
The platform offers a number of features available that expand the financial positions you can take - for example the ability to short Bitcoin via margin trading. The exchange also offers a set of other cryptos apart from bitcoin such as Litecoin and Ethereum.
Deposits and withdrawals take place via the standard bank transfer means with fees of 0.1% and a minimum of $20. Bitcoin and Litecoin are free. BitFinex takes security seriously and have moved from a hot wallet cold wallet set up to segregating customer funds where each user has access to their own wallet which they can review on the blockchain.
Bitfinex was hacked on 03 August 2016 and around 120,000 BTC were stolen.