Translation:We will arrive on Tuesday.
We arrived on Tuesday is a perfective statement: the action is completed. It should be translated povjaj mapawpu' or pojvaj mapawta' (or even povjaj mapaw rIntaH).
We will arrive, on the other hand, is not a completed action. Your point of view is from before the arrival. Notice, however, that We will have arrived takes the point of view of after the arrival, and so would be a completed action and translated with mapawpu' (etc.).
Unfortunately, this course does not correctly translate tense and aspect, so the correct sentences I have given above will not work in the software.