GRAC_S_USER_REF_USER is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "User 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_GRAC_S_USER_REF_USER TYPE GRAC_S_USER_REF_USER.
The GRAC_S_USER_REF_USER table consists of various fields, each holding specific information or linking keys about User name data available in SAP. These include REF_USER (User Name in User Master Record)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .