What is the syntax to create SORTED TABLE in ABAP ? If we created a SORTED TABLE, then how to INSERT work_area (=line) into it without specifying INDEX ?

When i try to insert work area ( =line ) to internal table of a SORTED TABLE With (or without ) unique key, I cant insert any lines to it without specifying INDEX.

I herd that "It is not required to specify INDEX while inserting work area to SORTED Internal table"

Is above statement true ...?