you're just as likely to win at slots online as you are in a real casino ie. not that likely.
 However if you do want to try then you simply deposit money in an account at the casino via one of a dozen or so methods - moneybookers, neteller etc. and when you win you can transfer the money from your casino account back into this account then into your own bank account.
For the best place for a US player to play slots have a look here. 

http://www.dashelc.com/slots-oasis-casino-review.html

hope this helps