On Birta, a version is a numbered, published state of a project. Every successful publish creates a new one, with a timestamp and an optional short note from the agent, and it immediately becomes the one answering at the project's public address.
Older versions do not disappear. Birta keeps the last ten, and any of them can be made live again as a rollback, without rebuilding the site from scratch. This is what turns a bad publish into a correction rather than an emergency.
A version starts life as a draft: the same files, before anyone said they were ready to go live.