Need clarification on PL/SQL Package

I have some doubt on PL/SQL Package. Please explain me, need your help for the below.

Please check the below program:
CREATE OR REPLACE PACKAGE valerr
IS
   FUNCTION private_variable RETURN VARCHAR2;
END valerr;
/

CREATE OR REPLACE PACKAGE BODY valerr
IS
   g_private   VARCHAR2 (1);

   FUNCTION private_variable
      RETURN VARCHAR2
   IS
   BEGIN
      RETURN g_private;
   END private_variable;

   PROCEDURE initialize
   IS
   BEGIN
      DBMS_OUTPUT.put_line ('Before I show you v...');
      g_private := 'abc';
   EXCEPTION
      WHEN OTHERS
      THEN
         DBMS_OUTPUT.put_line ('Trapped the error!');
   END initialize;
BEGIN
   initialize;
END valerr;
/

Now Please explain me on my below points:
1. When i am login through a new session, only specification will be loaded in SGA or both body or specification or specification and Declarative part of body.
2. When the body will be loaded.
3. What is the internal process of Oracle when we are executing a procedure of a package.

Thanks in advance