BAPI_0051_FIELDS 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 "Single fields parameters for Budget Data - Method SetTotals" 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_BAPI_0051_FIELDS TYPE BAPI_0051_FIELDS.
The BAPI_0051_FIELDS table consists of various fields, each holding specific information or linking keys about Single fields parameters for Budget Data - Method SetTotals data available in SAP. These include FISC_YEAR (Fiscal Year), VERSION (Budget version), BUDCAT (Budget Category), GET_PERIOD (Period data required)... 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. .