Simply put:
As you already said, stuff that is internal to us (such as our own bodies) is owned by us. Likewise, anything we produce using our own bodies (work) is ours. We can exchange the work we do for stuff that others have made with their own bodies (a simple form of bartering). Since bartering in this day and age is rather cumbersome, we have monetary systems which create a valid medium of exchange that can be used instead.
So in effect, we exchange the work we do for money, and the money we have for things that other people have worked on.
As you already said, stuff that is internal to us (such as our own bodies) is owned by us. Likewise, anything we produce using our own bodies (work) is ours. We can exchange the work we do for stuff that others have made with their own bodies (a simple form of bartering). Since bartering in this day and age is rather cumbersome, we have monetary systems which create a valid medium of exchange that can be used instead.
So in effect, we exchange the work we do for money, and the money we have for things that other people have worked on.
