PSO57 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 "Available Fields for Fixed Values on Request Screens" 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_PSO57 TYPE PSO57.
The PSO57 table consists of various fields, each holding specific information or linking keys about Available Fields for Fixed Values on Request Screens data available in SAP. These include KNAMID (Name of a Subledger Account), LIFNR (Account Number of Vendor or Creditor), LNAMID (Name of a Subledger Account), NAMID (Name of a Subledger Account)... 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. .