Okay, your payment agreement is a contract you make with the school that details how you will handle the financial aspect of it.
When they list "Payment in Full", they mean that they require you to pay that entire 12000, in full.
Let me use mine as an example.
My fees are coming to $7222.
My OSAP money is over 9 grand.
On my payment agreement I checked "Payment in Full".
When my Payment Agreement updated itself, I was informed that the school was going to take some 5000 from my OSAP money and I would have to pay them $1650 in September to avoid interest.
My OSAP is being released in 2 installments, like your's and everybody elses.
I will receive 60% in September, and that goes directly toward my fees.
I pay $1650 out of my own pocket UNLESS I have a scholarship that I can use to cut that down. Let's say I have the most basic entrance scholarship which is a $750. When that shows up as a payment option in August, I can select that and will only have to pay $900 in September.
When my mum pays that $900 in September, she does that through her own bank.
In January, I get about $3000 from OSAP (the rest of my release.)
I give her $900 back and use the rest as I see appropriate to meet my university expenses
I hope that helps because the others covered your other questions