In June, Google announced that screen mirroring was coming to the Chromecast dongle. The update that makes it possible has now been released. However, it only works with the most recent Android smartphones and tablets.
Screen mirroring with Chromecast
Screen mirroring allows you to mirror your Android device screen onto the TV wirelessly. It has been possible with Chromecast and a PC since launch, but this is the first time it has been available on an Android device.

However, you need a recent Android device to do so, and several manufacturers are still missing from the official list. To mirror your screen you have to download the Chromecast app and press the “Cast screen” button.
The Chromecast app for Android can downloaded here.
Mirroring is supported on the following devices:
Nexus 4
Nexus 5
Nexus 7 (2013)
Nexus 10
Samsung Galaxy S4
Samsung Galaxy S4 (Google Play Edition)
Samsung Galaxy S5
Samsung Galaxy Note 3
Samsung Galaxy Note 10
HTC One M7
HTC One M7 (Google Play Edition)
LG G3
LG G2
LG G Pro 2