Calling an oracle package function with an clob output

So I created a simple procedure to try and call with no luck. This is so easy to do in Microsoft. I am actually wondering now if you can even call procedures from SQL Dev. Are there add ons I need to the oracle database to accomplish this.

create or replace procedure My_login( IN_User_id number,out_p out varchar2)
is
begin
select app_users.user_name into out_p from app_users where user_id =IN_User_id;
end My_login;


--Call to procedure
set serveroutput on;
Declare
Answer varchar2(100);
begin

My_login(1976, :Answer);
dbms_output.putline(Answer);

End;