When trying to add a new station to your organisation, you will be asked to provide its identity.
The identity of your charging device is basically its unique name. It does not have a predefined format and is often defined by the manufacturer, either according to their own specifications or the ones of their customer.
If you have just purchased a charging device, you should be able to find it from the box it came in. The identity can be sometimes also be called Chargebox ID (in short CBID), IMEI number, or ACU name.
If you are dealing with a device you can't easily find this information from just by looking at it, you will find that information when connecting yourself to the station's software (locally or via a remote tool provided by the charger manufacturer), usually in the General Settings.