The plan here would be to freeze energy bills at the current level for this winter and the next but the catch here is that they are to be paid for by government-backed loans to energy supplieres. So, what's going to happen next? BBC reports that "those loans would be repaid over the next 10 to 20 years through supplements to customer bills". To cut short, it is households who will have to pay for them eventually i.e. the cost is just being spread out instead.
Truss' scheme is said to possibly cost beween £100 to £130 billion.