If you are looking for obtain Map API for debug on emulator in your local development platform, refer to the article "Obtaining a Maps API Key, for debug".
If you are going to deploy a Android application with MapView, you have to obtain a Maps API Key for Your Signing Certificate.
You have to get the MD5 Fingerprint of Your Signing Certificate. Refer to last article "Sign and deploy Android App", you know where is your keystore and alias. Start a Terminal, switch to the folder of the keystore, type the command with your own alias_name and my-release-key.keystore.
$ keytool -list -alias alias_name -keystore my-release-key.keystore
Now you can log-in with your Google account and go to Sign Up for the Android Maps API.
Accept the terms and conditions, fill in with your MD5 fingerprint, and Generate API Key.