FRMLS_HDR_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 "RMS-FRM: Formula 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_FRMLS_HDR_DATA TYPE FRMLS_HDR_DATA.
The FRMLS_HDR_DATA table consists of various fields, each holding specific information or linking keys about RMS-FRM: Formula Header Data data available in SAP. These include MARKFLG (Row Is Selected), SELEFLG (Step Loop Line Selected), LINENO (General Auxiliary Counter), LINEMOD (Processing status or mode of a record/step loop line)... 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. .