D1209 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 "Maintenance Field Structure, Task Cost 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_D1209 TYPE D1209.
The D1209 table consists of various fields, each holding specific information or linking keys about Maintenance Field Structure, Task Cost Data data available in SAP. These include MANDT (Client), PLVAR (Plan Version), OTYPE (Object Type), OBJID (Object ID)... 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. .