Unzip and flash the image on the SD card with Etcher or dd. Boot and log in to the Raspberry Pi with ssh pi@poppy.local, the default password is raspberry.
You can then start ROS Poppy services with roslaunch poppy_controllers control.launch and take control over it with MoveIt or Python.
Be careful, this image won't serve the regular puppet-master user interface (http://poppy.local) on the Poppy Ergo Jr, it is only a ROS image.