I'll try to help, I did this for the first time a few days ago.

After adding Bitstamp as a BTC issuer, you need to "trust" them to exchange the ripple BTC IOU's for genuine BTC.  This is done by Advanced --> Trust --> Green + sign, then paste the ripple address of Bitstamp and click save.

After that, on the left hand side, click Trade, use the dropdown to choose BTC/XRP.  Click Order Book near the bottom of that page and you should see a fairly active order book like you would at a Bitcoin exchange.