Step 1: Install PhoneGap
The PhoneGap Desktop application provides a drag and drop interface for creating PhoneGap applications. It's an alternative to using the PhoneGap CLI built for those who prefer a visual user interface over a command line interface approach.
Select your operating system to continue:
Mac OS X Installation
Download the latest Mac OS X Installer.
Double-click the downloaded file to run the installer. You will initially be prompted with a license agreement to accept:

Drag and drop the application into the Applications folder on your Mac as prompted:

Next simply open the application and proceed to Step 2 where you will install the PhoneGap Developer App to your mobile device for previewing the apps you build.

Windows Installation
Download the latest Windows Installer.
Double click the downloaded file to run the installer. You will be prompted with the PhoneGap Desktop Setup Wizard:

Accept the license agreement:

Select the desired destination for the application and click Next:

Select the desired location for the shortcut and click Next:

Click Install to begin the installation:

Click Finish to close the Setup Wizard:

Next simply open the application and proceed to next step below where you will install the PhoneGap Developer App to your mobile device for previewing the apps you build.
