Your Drupal site will consist of three environments:
A development enviroment with a URL of site.dev.umn.edu (or site-dev.umn.edu)
A staging environment with a URL of site.stg.umn.edu (or site-stg.umn.edu)
A production environment with a URL of site.umn.edu
where site is the alias of your site.
This site is usually used for developing code such as sub-themes or custom modules. This is the environment where the developer will upload, de-bug, and troubleshoot code.
When the developer is done with coding a site, you will move it to the staging environment for testing. In this environment contributors, site managers, and other stakeholders will verify that the code works as expected. In order to do this, they usually want to test with live data so you will need to copy the database from production to staging.
When you first migrate to Drupal, the staging environment is also where your migrated content will be loaded and tested before moving to production.
This is the public facing site where people go to consume your content. This is also where the contributors add content to the site.
Moving site data between environments
It may sometimes be necessary to copy the site from one environment to another. An example would be adding a new module after a site has been launched. The module should be tested in the development environment, but needs to be tested against content that only exists in the production environment.
You can request that site data be copied between environments by sending an email to firstname.lastname@example.org. Include the name of your site, the source environment (where you would like to copy from) and the target environment (where you would like to copy to).