You agree to buy the home from the seller over time. You make regular payments to the seller. You don't own the home until the contract is complete.
An instalment sale agreement between you and a credit provider allows you to buy a vehicle or asset using the principal debt, which you repay by means of regular instalments over an agreed period, with fees and interest.
In fact, they'll likely ask for documentation of any accounts that hold monetary assets. This is because mortgage lenders want to know that you'll be able to afford your down payment – if one is required – and make your monthly mortgage payments.