The property is fully yours from day 1, but if you sell before yr 10, you have to repay in full the percentage discount you originally got, ie if the property market price when you bought was €300k but you only paid €200k, you'd have received a discount of 33% and would have to give them 33% of whatever sale price you achieved.
After year 10 the amount repayable to them decreases by 10% per annum, so that in yr 15 for instance you'd only have to repay 50% of the initial 33% discount, and by yr 20 you pay them nothing if you sell.