SALV_SERVICE_S_LAYOUT is an SAP Structure so does not store data like a database table does but can be used to process "ALV: Service Level" 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_SALV_SERVICE_S_LAYOUT TYPE SALV_SERVICE_S_LAYOUT .
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|
|T_LEVELS||SALV_SERVICE_T_LAYOUT_LEVEL||TTYP||ALV: Layout Levels|