SIMP000 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 "IMP: Application Classes - Basic Data - Screen Structure" 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_SIMP000 TYPE SIMP000.
The SIMP000 table consists of various fields, each holding specific information or linking keys about IMP: Application Classes - Basic Data - Screen Structure data available in SAP. These include APPLCLASS (IMP: Application Class), LANGU (Language Key), SHORT (IMP: Short Text - General)... 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. .