If you want to use or pass selection options into your SAP function modules you can use table type RSELOPTION which has the line type of RSDSSELOPT.
This field can then be used directly as a select option for selecting data from a table. See example below of how the ABAP code will look within a function module.
*" IMPORTING *" REFERENCE(I_EBELN) TYPE RSELOPTION OPTIONAL data: it_ekko type standard table of ekko wa_ekko like line of it_ekko. select * from ekko into table it_ekko where ebeln in i_ebeln
Also see table type BAPI_RE_T_SELOPTION if you want to pass multiple select-option fields using the same parameter.
BSEG select performance improvements
SAP Sales Order Table data in SAP ( Sales and Distribution module)
SAP CRM Tables within the data dictionary and their relationships
Create new HR Infotype record ABAP Code
SAP Purchase Order tables