How do I Japanese in my computer?

If you use windows, open the control panel. Open Clock, Language and Region panel. Look for the task that says something along the lines or changing/adding keyboards or input methods. A new box will pop up click the button that says, to change or add keyboards (it's the only one there) when yet another box comes up, it shows the installed keyboards. Find the button to the right that says, 'Add' and click it. Search for Japan, and add it and press ok. When it goes back to the installed keyboards, Japan should be there and if you look at the task bar down the bottom to the right there will be a little thing that says EN, click on this until the box comes up offering other language and click JP. A new menu type thing will open up, and you can choose your method of input. English like this, or hiragana or katakana. Once you've done what you wanted, just remember to change it back to english.

You have to install Japanese IME.

http://www.declan-software.com/japanese_ime/

MSIME shall be installed into yr PC for making Japanese text if it is Windows.