FMDI_HEADER 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 "Direct Input from Budget: Document Header Data" 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_FMDI_HEADER TYPE FMDI_HEADER.
The FMDI_HEADER table consists of various fields, each holding specific information or linking keys about Direct Input from Budget: Document Header Data data available in SAP. These include TCODE (Char 20), FM_AREA (Financial Management Area), VERSION (Planning/budgeting version), FISC_YEAR (Character field, length 4)... 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. .