After you select your favorite languages from the settings, Google downloads the language packs. The English files are preloaded, so there's nothing to download. By the default, handwriting recognition works offline, but you can tap the cloud button to switch to the online recognition mode. Here's a help center page that offers more information about Google Handwriting Input.
Google Handwriting Input works like a regular Android keyboard, so you can use it any Android app that lets you input text. Google automatically converts your handwriting to a text and shows some other candidates (long press the centered candidate to see even more suggestions). If you try to write a word that's too long, you can type the first part of the word and then continue entering the rest of the word, as Google's app is smart enough to merge them. You can also write two lines or switch to the landscape mode.
"By building on large-scale language modeling, robust multi-language OCR, and incorporating large-scale neural-networks and approximate nearest neighbor search for character classification, Google Handwriting Input supports languages that can be challenging to type on a virtual keyboard. For example, keyboards for ideographic languages (such as Chinese) are often based on a particular dialect of the language, but if a user does not know that dialect, they may be hard to use," informs the Google Research blog.
Google's app claims to support even terrible handwriting, but that's not always the case. Sometimes a poorly written letter can make the app return incorrect results, especially for less common words.
Google Handwriting Input requires Android 4.0.3 or later and works for both phones and tablets. It integrates many features that were previously available in other specialized Google apps and services (Mobile Google Search, Google Translate for Android and iOS, Google Input Tools for Gmail, Google Docs and Google Translate, Gesture Search for Android, Input Methods for Chinese, Cantonese and Hindi).