Wait, are you saying that "iru" is the natural form and that "te" is the present/future tense? In that case, what does iru represent. I'm sorry, I'm just trying to get a solid understanding. I started like three days ago lol.
As for Rosetta, I understand it's not the end all of language solutions, which is why I bought several textbooks which are coming in the mail. Rosetta is a bit lacking when it comes to the rules of the language.