Why do humans poo and pee?
After you digest your food, your body takes the nutrients from what you eat and creates it into energy for your body. The leftover food your body doesn't need will come out as poop or pee.
Same as any other rabbits, if you want it to only pee/poo in its cage, then when you first buy your rabbit, don't let it out of its cage for a week or so, so that during that time it will only pee/poo in its cage and regocnize that it's the place to pee/poo. And if it goes pee/poo outside, scold slightly "No" and gradually it will understand what "No" means lol. At least this…
You have to train it not to do this by punishing it when it does by squirting water at it or putting it outside for a while. Keep doing this until it understands that it cant pee or poo inside. When ever you see it pee or poo outside, reward it by giving it a treat. In some time it should learin not to pee or poo in the house.