*For example i have used the scarr table
*Internal table declaration.
Data: Begin of Itab occurs 0,
      carrid like scarr-carrid,
      carrname like scarr-carrname,
      currcode like scarr-currcode,
      end of itab.

*Fields on selection screen.
parameter : carrid for scarr-carrid ,
            carrname for scarr-carrname,
            currcode for scarr-currcode.

*To insert data from Selection screen fields to the 
*internal table
loop at itab.
itab-carrid = carrid.
itab-carrname = carrname.
itab-currcode = currcode.
append itab.
clear itab.
endloop.

Just by looping you can insert multiple data to the 
internal table. Let me know if this code worked for you.