WCSALV21 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 "WCM: Operational Class <-> Technical Object" 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_WCSALV21 TYPE WCSALV21.
The WCSALV21 table consists of various fields, each holding specific information or linking keys about WCM: Operational Class <-> Technical Object data available in SAP. These include CCOBJ (Technical Object), CCTYP (Item Category), TGCLASS (Operational Class), DBFLG (Data base indicator)... 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. .