I'm going to go a bit more broad with answering that [kandyman](https://japanese.meta.stackexchange.com/a/1958/1010) did.

In general, these are called [IMEs](https://en.wikipedia.org/wiki/Input_method).  This is software you use to actually translate what is commonly seen as Romaji into actual Hiragana, Katakana or Kanji.

I won't make any recommendations since that's not really my intention here, but I will say this:

**Using an IME does not mean you're now able to *proficiently* type Japanese.**

Converting between Kanji, Hiragana and Katakana is a many-to-many match, and while most common phrases and expressions may be filled in, you have to know and understand the context of what characters are actually being displayed on-screen.  Otherwise, what you're typing will be confusing or indiscernible to someone else.

It's the difference between typing 間に合いそう (let's make it on time) or マニアイソ (mania).