MSTSD 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 "Structure for transferring milestone data to SD" 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_MSTSD TYPE MSTSD.
The MSTSD table consists of various fields, each holding specific information or linking keys about Structure for transferring milestone data to SD data available in SAP. These include MLSTN (Usage), TEDAT (Scheduled milestone date (Basic)), TPDAT (Scheduled milestone date (Forecast)), SDDAT (Key determining the date for milestone in sales order)... 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. .