When you start NexusDB server for the first time, you will see a NexusDB icon in the system tray and a message asking whether you want to install the service or not. If you confirm the service installation you will be prompted for a user account and password for the service to run under. The user account is expected as domain\username, but you can use "." to specify the current or default network domain (eg .\username).
For the service to run/start successfully the chosen user account must have the "Logon as service"right, otherwise you will get an error when trying to start the service. Please see the instructions here.
NexusDB V3.01 introduces a number of server command line parameters that can be used to create new users and set privileges.
Once you've confirmed the username, you will get a message that the service was installed and whether you want to start the service. The service is per default installed as "Automatic" which means that it will automatically be active after a Windows start, even if no user is logged on.
The server is now running as service and you can use the tray icon to open the Administration by selecting the Config menu item.
If you need more control for example running multiple NexusDB server instances on the same machine, please take a look at the command line paramters.
Also note that it is normal to see two nxServer.exe processes running in Task Manager when nxServer is installed as a service. One instance handles the tray icon, and the other is the database server service.