Hi Angela,
online casino bonuses are tricky little things and im sorry to say it all depends on which casinos you play at, so unfortunately that means reading a lot of small print. Some casinos offer risk free bonuses whereby you may deposit and withdraw at any time, others are not so kind. In response to withdrawing your winnings before fulfilling your wagering requirements a lot of online casinos state in there small print that if you will forfeit any winnings if you attempt to withdraw your money before fulfilling your wagering requirements, so be careful.
a useful piece of software that you can download fro free can be found at
www.bewisebets.co.uk/software/blackjack
it is a bj calc that will give you the optimum strategy for playing blackjack online, simply choose the software the casino runs on and play away, also included is a list of casinos that allow you to play blackjack with your bonus money, as many casinos now forbid it.
Hope this helps and good luck