When you first get started you have one or two canned images to play around with but this is probably not much use beyond kicking the tires and confirming that you have your configuration working properly. Inevidably you will need to add some pre-existing images or create your own, it is pretty easy to get started based on the current offerings from different OS vendors today to start with your favorite base OS and work from there.
If you have not already read some of the docs, take a look at the Chapter 2. Get Images1. This page contains links for downloading various images from Cirros, CentOS, Fedora, Ubuntu, Debian, and Windows
- docs.openstack.org - Chapter 2. Get Images