You can write anything you want; the payout you can get from your posts depends a lot of the number of votes and promotions. Another way to earning money is commenting, upvoting, resteeming and promoting contents.

Now, you receive the payment in (in Steem Dollars [SBD] and STEEM by the way) your wallet. From your wallet you can transfer to any exchange like Poloniex, Bittrex, and Kraken, where you convert the SBD and STEEM into Bitcoin. Once you have your satoshis (bitcoin cents), you can transfer them to another wallets like Coinbase.