STR_MLST 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 "MIlestone with read indicator:wbs/activity" 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_STR_MLST TYPE STR_MLST.
The STR_MLST table consists of various fields, each holding specific information or linking keys about MIlestone with read indicator:wbs/activity data available in SAP. These include MLST_MANDT (Client), MLST_ZAEHL (Milestone number), ZAEHL (Internal counter), DATUV (Valid-From Date)... 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. .