The Administration section on the RTS Wikia is tutorials on how administration takes place on the server. Though designed for admins, everyone has access to see and view this, and provides a behind the scene look at what goes on.
The registry is a semi automatic system that works as a status call board for trains in the cycle. It works with Google Sheets and is also displayed on the Wikia in the link above. Because registry commands are open to everyone release and build commands can be entered by anyone. However only an admin can authorize the use of these commands.
With that being said in order to make trains available for download, the admins must on a regular basis release trains into the cycle. When a release command is issued, the registry will not only show release but also provide access to the download link. This is where anyone wishing to spawn a train can download, spawn, and run a train from the entrance to a route from the border. Releasing can also be applied to yard trains that have been built. Like other releases, this allows the admins to control the flow of the cycle. However no download link will show up for a train originating in a yard, since it is not a spawn and has been built.
Speaking of builds, setting a train to build authorizes yard crews authority to build a train. It's important to ensure that all practical cars used to build the train has arrived before issuing this command. Keep in mind some trains can be delayed, while others who are prerequisites for other trains down the line can not.
Generally we try and provide as much variety to the users as we can. However we must also provide balance to other areas. If one area is getting more trains running than another, the admins must scale back what it releases from the more popular section. To help keep track of where we are in a cycle, the actual call times are provided where applicable. These times of course are based on the position in the cycle and not the actual sim time. This of course will change down the road once AI is on board as more trains will be running all the time. The following is a video I put together is an example of some releases and builds earlier tonight before I wrote this article