FMFMSU2 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 "FM: Internal Reporting Structure" 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_FMFMSU2 TYPE FMFMSU2.
The FMFMSU2 table consists of various fields, each holding specific information or linking keys about FM: Internal Reporting Structure data available in SAP. These include LEDNR (Budget/Planning Ledger), OBJNR (Object number), GJAHR (Fiscal Year), PERIO (Period)... 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. .