In the early days of Android, the Google Search app was limited to a simple text box which you could use to search the web. But over the past several years its feature set has grown larger than ever. The current version of Google Search app lets you search the web, your music library, your Chrome history and apps on your device. Voice search and the "OK Google" hotword lets you search the web — or your own stuff — by talking to your phone. Google regularly adds new voice commands to its Search app.
In Android 4.1 and above, Google Now (accessible by swiping up from the home key on some phones) introduces predictive search into the mix. Google Now shows you weather details, public transit times, upcoming flight details, driving directions for upcoming appointments and scores from sports teams you follow.
And with the Google Now Launcher — available as a separate download — the Google Search app takes over your home screen, putting Google Now within easy reach as the leftmost home screen panel.
Because of its expanded feature set, and its presence on the default home screen of every Google-certified Android device, Google Search is one of the most important applications in Google's mobile services arsenal.