This feature is easily identifiable by clicking on the Microphone logo icon in the Google search bar. Google posted the release on her Google+ page on 23rd May 2013.
You can now start to have a conversation with search on all your devices—including your desktop or laptop. We’re rolling out the new conversational search functionality over the next few days in +Google Chrome, so you can ask Google about “Italian restaurants in San Francisco” and continue the conversation with “how about Chinese." Or find out “who is the prime minister of Australia” then ask “how old is she”—and Google will give you a spoken answer. Just click the mic in the Google search bar and speak up. Also, be sure to have the volume up on your computer to hear your answer loud and clear.Visit Here for more.