Amazon has finally made Alexa available to android devices, instead of making it a standalone app the have added it to the shopping app presumably to encourage users to purchase more things. To access Alexa you need to head to the Google Play Store and download the Amazon shopping app.
Once the app has downloaded open the app and you will see a microphone icon in the upper right corner, above the search bar.
Once Alexa is enabled, tapping the microphone will automatically cue up the voice assistant, and you can begin speaking a command. Just as with the Echo if you don’t issue a command within a second or so, Alexa will timeout.
Using this icon you can do things like listen to the news, stream music from Amazon Music, listen to your audiobooks, have Alexa read your Kindle books to you, control your smart home. Users are also able to use the icon to Play games and enable skills.
Other ways to experience Alexa for Free is currently through Amazon.com where you can purchase the Amazon dash wand for $20 which comes with a $20 credit.