Why? Just go outside and ride your bike for f**k sake! !!!!
Because that isn't always an option.
Where I am, I'd have to do about half an hour to get outside of the city to roads worth cycling on, then they are dead flat. I'd have to do the same half hour to get back, so that's an hour before I've really started my ride. If I want to take in a single hill, it's a 53km round trip.
The OP is in the southern hemisphere, so it's winter there at the moment, not ideal cycling weather. Maybe they too would have to spend too much time getting out the city to where they can cycle? Maybe they just want to see what it is they have signed up for. Maybe it's pan flat, or steep mountains there. Maybe they don't want to ride at the moment as they would spend the whole time dodging dive bombing birds (real issue in WA).
In short, why don't you either post constructive stuff, or shut the fuck up. People have their reasons for asking questions, even if they might not make sense to you. This is the OP's first post, and being told to just ride their fucking bike, is quite frankly, unwelcoming bullshit.
So, to our new Aussie forumite, I can't offer you any help with your tacx trainer as I don't have one, but welcome to the forum, and I hope you can get some useful answers to your questions. We're pretty friendly round here, honest.
J