FMGLFLEX03_DATA 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 "General Ledger: Additional Acct Assignmt in Data Part of LIs" 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_FMGLFLEX03_DATA TYPE FMGLFLEX03_DATA.
The FMGLFLEX03_DATA table consists of various fields, each holding specific information or linking keys about General Ledger: Additional Acct Assignmt in Data Part of LIs data available in SAP. These include KOKRS (Controlling Area), FIKRS (Financial Management Area)... 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. .