So, from there, you need something to learn. I would recommend using a comprehensive system (like a beginner textbook with CDs or an online lesson program). That will take you through beginner grammar and vocabulary in an ordered manner. It is hard to just study random information. Better to have a syllabus or plan to follow. Then, once you have studied a little bit, you will have something to talk about with your teacher or language partner. I like the japanesepod101 site a lot because it breaks everything down into easy 15 minute lessons. If you are more in the mood for a textbook, "Genki" or "Minna no Nihongo" might be good. Either one should be available from Amazon. Good luck!

That's great you know katakana and hiragana! The next step that I recommend is to find a native japanese teacher here in Italki and a language partner. Most teachers here have trial lessons :)