SSPIUSRNAM is an SAP Structure so does not store data like a database table does but can be used to process "SPI: Assignment of User Name to Display Name" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately.
i.e. DATA: wa_SSPIUSRNAM TYPE SSPIUSRNAM .
Below is the documentation avaialable and full details of the fields which make up this Structure.
|Data Type||length (Decimals)||Check table||Description||Conversion Routine|
|SAPNAM||SPISAPNAM||CHAR||12||Logon Name of User|
|DISPLAY_NAME||AD_NAMTEXT||CHAR||80||Full Name of Person|