You have $100 worth of Hive, SPI or Leo. You send that to @bearbonds, that sends you $100 worth of Bear Bonds - these represent the loan.
You send the Bear Bonds to @bearbonds which releases $100 worth of HBD to you. You have many choices now:

• save and gain 12% interest.
• use to purchase other second-layer tokens.
• exchange for fiat.

At the end of the loan period, assuming your original tokens have held their value, you buy sufficient Bear Bonds to repay the loan and send them to @bearbonds to release you Hive, SPI or Leo.
You can also buy Bear Bonds weekly during the loan period using the recurring payment mechanism on Hive, so you are gradually putting aside the amount to repay the loan.