1. In the tab Dbms Output choose:
   
2. Chose the connection:
   
3. Running a small test:

   DECLARE
   BEGIN
     DBMS_OUTPUT.PUT_LINE('boo');
   END;
   /
   

Съответно нашия низ бива отпечатан в конзолните прозорци Script Output и Dbms Output:

anonymous block completed
boo