This loses some subtleties, and bear in mind that the entire passage is a question, which Rousseau then goes on to expand upon and answer. He uses a rhetorical device, stating a series of things which seem contradictory, but which are completely logical in the context of the Social Contract. I have capitalised The State throughout in an attempt to make it clearer. (Please edit if I've missed something, I've rushed through this quickly)
How is it possible that people can be free if they are subjects of The State?
The people that make up The State are made use of by The State without
any constraints. The State does not explicitly ask what they, as
individuals, want: The State uses them, their lives and their property
freely, without consulting them.
The State, by its own admission, prevents them exerting their own free
will, and the people consent to this.
Their will is therefore that of The State. If they refuse to consent to what the state wishes, then they are acting against their own will. If they act against The State, they (seemingly willingly) punish themselves.
It doesn't quite mean "Is there anything that can make men free by forcing them doing what they do not want to?", rather it is asking how people can be free if they are subjects of the state (the answer being that the people are the state). Subtle difference, but important in context.