COPA999 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 "Example Structure for Transferring External Data to CO-PA" 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_COPA999 TYPE COPA999.
The COPA999 table consists of various fields, each holding specific information or linking keys about Example Structure for Transferring External Data to CO-PA data available in SAP. These include BUMON (Number of periods per seasonal cycle), ALTPERIO (Period/year in alternative period type), VRGAR (Record Type), WADAT (Goods Issue Date)... 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. .