So, that's great, it worked.
I would have never guessed the format.
But now i have a problem. With that format, i stored the value in v_t1.
How do I show the contents with dbms_output?
Thanks in advance.

SQL> set serverout on
SQL> DECLARE
  2  v_t1 T1_TAB;
  3  BEGIN
  4  v_t1 := T1_TAB(
  5    T1_OBJ('Hernan',NULL),
  6    T1_OBJ('Connor',5),
  7    T1_OBJ('Mike',10),
  8    T1_OBJ('Susie',NULL)
  9    );
 10
 11   for i in 1 .. v_t1.count
 12   loop
 13     dbms_output.put_line(v_t1(i).field1);
 14     dbms_output.put_line(v_t1(i).field2);
 15   end loop;
 16
 17  END;
 18   /
Hernan
Connor
5
Mike
10
Susie

PL/SQL procedure successfully completed.

Thanks Oracle gurus.

I had created my object types in the following manner :

CREATE OR REPLACE TYPE o_obj_a AS OBJECT
( field_1a VARCHAR2(20),
field_2a VARCHAR2(20)
);
/

CREATE OR REPLACE TYPE o_obj_a_t IS TABLE OF o_obj_a;
/

CREATE OR REPLACE TYPE o_obj_b AS OBJECT
( field_1b VARCHAR2(20),
field_2b VARCHAR2(20)
);
/

CREATE OR REPLACE TYPE o_obj_b_t IS TABLE OF o_obj_b;
/

CREATE OR REPLACE TYPE o_obj_c AS OBJECT
( field_1c VARCHAR2(20),
field_2c VARCHAR2(20),
a_details o_obj_a_t,
b_details o_obj_b_t
);
/

CREATE OR REPLACE TYPE O_OBJ_C_T IS TABLE OF O_OBJ_C;
/

I wanted to initialize all the object types but I wasn't able to do so through an anonymous block. This is where your block helped me out.

set serveroutput on ;
DECLARE
a_details o_obj_a_t;
b_details o_obj_b_t;
c_details o_obj_c_t;
BEGIN
a_details := o_obj_a_t(o_obj_a('a_data1','a_data2'));
b_details := o_obj_b_t(o_obj_b('b_data1','b_data2'));
c_details := o_obj_c_t(o_obj_c('c_data1','c_data2',a_details,b_details));
FOR i IN 1..c_details.COUNT
LOOP
DBMS_OUTPUT.PUT_LINE('Field 1 of C : '||c_details(i).field_1c);
DBMS_OUTPUT.PUT_LINE('Field 2 of C : '||c_details(i).field_2c);
DBMS_OUTPUT.PUT_LINE('Field 1 of A : '||c_details(i).a_details(i).field_1a);
DBMS_OUTPUT.PUT_LINE('Field 2 of A : '||c_details(i).a_details(i).field_2a);
DBMS_OUTPUT.PUT_LINE('Field 1 of B : '||c_details(i).b_details(i).field_1b);
DBMS_OUTPUT.PUT_LINE('Field 2 of B : '||c_details(i).b_details(i).field_1b);
END LOOP;
END;
/

Got my output :

Field 1 of C : c_data1
Field 2 of C : c_data2
Field 1 of A : a_data1
Field 2 of A : a_data2
Field 1 of B : b_data1
Field 2 of B : b_data1

PL/SQL procedure successfully completed.

Thanks once again. :)