Secured debt means a lender gives you money in exchange for what?

Typically, the borrower makes a Promissory Note which pledges or agrees to pledge some asset as collateral and also sets the terms for paying interest and principle. If the lender is a bank, it is typically advancing you its own credit (the check) in exchange for you extending your credit to it (your Note). The bank ideally gets interest and you get purchasing power you wouldn't otherwise have if you attempted to give your IOU directly to a merchant.