Go to Acquia Downloads and download a release for your operating system.
Run the installer:
If you can’t open it by double-click in OS X, right-click it and select open.
Select Open again:
Use the default settings and finish the installation.
Select start from scratch to add a new site:
You will be offered bunch of distributions, select the official release:
Leave the default settings and select Finish:
Navigate to the site address to finish the installation:
Check How To Install Drupal With MAMP tutorial for info about the last state of the installation.
And there you go: