You send $10,000 to a Canadian bank (plus a processing fee) and they deposit it into an account for you. Then every month for your first year in Canada, they send you back about $833 to pay for your living expenses, so by the end of the year you will have gotten your $10,000 back.
You need one to apply for a study permit under SDS because it proves you will be able to afford your living expenses in Canada, as the bank has already received and guaranteed the funds, and you won't be able to spend all the money at once. The banks like it because you're effectively giving them a low-interest loan.