How to connect to another db using stored procedures?
You want to use a Database Link (DBLink). 

http://www.stanford.edu/dept/itss/docs/oracle/10g/server.101/b10759/statements_5005.htm

http://psoug.org/reference/db_link.html

-- create tnsnames entry for conn_link
conn_link =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = perrito2)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = orabase)
    )
  )


CREATE DATABASE LINK conn_user
USING 'conn_link';

SELECT table_name, tablespace_name FROM user_tables@conn_user; 


@conn_user on the end of a procedure or table name will tell the pl/sql engine to query the db link specified for that info.