Yeah the site is confusing. You first send the btc to your trading wallet, then you borrow BTC in the Lending section, then you put in a sell order up to your max leverage. The wallet/$ details look confusing to me - all I know is I borrowed 1BTC at 12% per annum.
60 days from now. You can "close" your position in one click which sends a market order to Gox, or you can re-buy manually with a limit order, then you pay back the lender.