how do you use DAZ 3D?
do you have to buy assets or is it possible to do it free?
how do you make rooms?
DAZ3D comes with some free assets but they are not many and you will probably be using them only to test out the program and learn it.
You can purchase assets or you can get free ones, DAZ3D sometimes offers free ones but you will find most of them from external sources, here is a link that contains most of them:
You must be registered to see the links