The easiest way to get started immediately, is to type in Manglish at one of many websites. And that is sufficient for most people. Our favorites are
- Varamozhi for its awesome keyboard map always available onscreen
- Aksharangal for its instantaneous transliteration. And a bonus point for being able to transliterate pasted text. Many other websites require you to type in the text.
There are a few more websites. They all seem to use the Transliteration engine created by Google. So the output is all the same. You can find them by googling for Malayalam typing transliteration.
In terms of convenience right at the point of use, nothing compares to the utility of Gmail. In Gmail, you can select the language and start typing in Manglish.