SELECT {function call} FROM DUAL;

SQL>  create or replace function f return varchar2 is begin return 'The result'; end;
  2  /

Function created.

SQL> var r varchar2(50)
SQL> begin :r := f(); end;
  2  /

PL/SQL procedure successfully completed.

SQL> print r
R
--------------------------------------------------------------------------------------
The result

orclz>
orclz> var n number
orclz> insert into dept values(50,'new','uk') returning deptno into :n;

1 row created.

orclz> print n

         N
----------
        50

orclz>