First download from our downloads page, then copy the Twixl Publisher.app from the disk image to your Applications folder. When opening this app, you will be prompted to install or update the InDesign plug-in if it has not been installed yet, or if it needs to be updated. The plug-in will then become available in InDesign from the menu Window -> Extensions. You also need to install the Twixl Publisher Helper.
In order to build iOS apps, Xcode and the latest iOS SDK need to be installed. For Android, the Android SDK needs to be downloaded.
Double click the Twixl Publisher.exe installer to install the plug-in for all supported versions of InDesign that are installed on your system.
The plug-in will become available in InDesign from the menu Window -> Extensions.