BAPI1138_GEN 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 "Interface Structure: General Fields" 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_BAPI1138_GEN TYPE BAPI1138_GEN.
The BAPI1138_GEN table consists of various fields, each holding specific information or linking keys about Interface Structure: General Fields data available in SAP. These include TESTRUN (Switch to Simulation Session for Write BAPIs), STATKEYFIG (Statistical key figure), STATKEYFIGGRP (Statistical key figure group)... 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. .