For reading Japanese in your computer you need a Japanese font.
You need an IME (Imput Method Editor) if you want to write Japanese.
You can find several Japanese fonts in this forum. Try searching for "Japanese font site:forum.koohii.com" in Google.
As for the Japanese IME, it depends on your operative system. If you don't know how to install it just write what OS you use and I'm sure someone will show you what to do.