Need help interpreting a part of Descartes' Sixth Meditation

In the Sixth Meditation, Descartes contends that he can know that there is a material world of objects outside his mind. What sorts of things can he know for certain about these objects? And their relations?


What I think Descartes is trying to say here is that all we can know is properties of extensions like motion, shape, size, number, weight. But I am not sure if that's totally true.

I would be glad if you can point me in the right direction with this question.