I think it is not so obvious, so I don't mind the question. Eventually I plan to make a new product wizard to make it more user friendly and it will create the product and the offer in one go.
There is also a module setting to determine whether your product list emphasizes offer or products. If most of your offers have one product then its better to emphasize products but if you are mainly selling offers with more than one product say albums of mp3 files then an offer emphasis is better.
Its flexible but a little cumbersome still. It will evolve over time to improve.
Best,
Joe