It's a complicated process right now that requires a few steps:

1. Transfering STEEM and/or SBD (Steem Dollars) to an Altcoin Exchange like Poloniex or Bittrex.
2. Use the Altcoin Exchange to convert STEEM/SBD to BTC
3. Setup an account on a BTC/FIAT exchange (like Coinbase or one within your country) and link it to your bank account.
4. Transfer BTC from Bittrex/Poloniex to a BTC/FIAT exchange
5. Use BTC/FIAT exchange to sell the BTC and then transfer the funds into your bank account

Steps 3-5 can be ignored if you just want to hold Bitcoin, which can be used to shop online many places (like overstock, newegg, or digital gift cards from gyft).

It's a lot better than it was a few years ago... but it's all still a bit of a pain.