As far as I know unless I've blatantly missed something you can't, steemdollars are an entirely seperate currency, what you could do though is sell them for steem and then for Bitcoin and then perhaps sell them for your local currency if you know somebody trustworthy to trade with.
Paypal is generally considered a bad idea for trying with cryptocurrency though because of reversible transactions, just a heads up.
so, how do I get them? for what can I use them?
Go to your wallet > Click on the drop down arrow where your steem dollars balance is > market
You should then be able to sell your steem dollars for steem and then transfer your steem out of there, steem dollars are just a peg to the dollar currency, they can be used in the steem store I think but I tend to just sell them for steem, not entirely sure why they're there to be honest but I hope the little tutorial helped.