NJ Star actually has components to transcribe into Japanese, but also Chinese and Korean as well. Be sure to download the correct version to make sure you are typing in the correct language. Also, if you noticed that upon opening NJ Star that you do not recognize what it is asking you to do, go to the Input or Help menus to ensure you are in the correct language.
At the bottom of the screen, in the left corner, you will need to choose the input/output method for what you type in will be. Choices are Romaji, Kana kanji, and Eisuu (English coding ASCII). With the exception of Romaji, these options are written in Japanese. You can run the cursor over them and an explanation will appear if you need it.
If you use Romaji, you will type in a word with the Romanized letters on your keyboard using Japanese pronunciation. You could type in hana, or flower, for example. Before anything appears where your cursor is on the screen, you will see several choices for the output pop up along the bottom of the screen. Your choices will be in either katakana, hiragana, and kanji or a mixture of kanji and hiragana. Each of the choices is numbered. You then hit the number for the choice you want to use. The writing for that choice will then appear on the screen and you will be free to move on to the next word.
Using Kana Kanji, you can type in the word in Japanese and see it appear immediately on the screen in hiragana. Using Kanji is much more complex with this function.
If you use the Eisuu function, you will be typing words in English with the standard English alphabet, or Japanese words in Romaji, just as you would if using Word.
To change the functions simply click on them and it will proceed to the next option.