Starting Backup Server depends on the platform you are running.
Most UNIX systems use the startserver utility to start Backup Server on the same machine as SAP ASE.
On Windows, start Backup Server from SAP Control Center. See the configuration documentation for your platform for information about starting Backup Server.
Use shutdown to shut down a Backup Server regardless of your platform. See System Administration Guide: Volume 1 > Diagnosing System Problems and System and Optional Databases and the Reference Manual: Commands.