End the current session or reboot your system.

Once you start a new session, verify that the
flutter command is available by running:

    
$ which flutter

For more details on setting the path in Bash,
see this StackExchange question.
For information on setting the path in Z shell,
see this StackOverflow question.

Android setup

Note:
  Flutter relies on a full installation of Android Studio to supply
  its Android platform dependencies. However, you can write your
  Flutter apps in a number of editors; a later step discusses that.

Install Android Studio

Download and install Android Studio.

Start Android Studio, and go through the ‘Android Studio Setup Wizard’.
This installs the latest Android SDK, Android SDK Command-line Tools,
and Android SDK Build-Tools, which are required by Flutter
when developing for Android.