CREATE OR REPLACE PROCEDURE insert_class(
  Teacher_name_param       class.teacher_name%TYPE,
  class_name_param         class.class_name%TYPE,
  Start_Date_param         class.start_date%TYPE,
  End_date_param           class.end_date%TYPE,
  class_category_param     class.class_category%TYPE,
  Topic_param              class.topic%TYPE,
  Teacher_credential_param class.teacher_credential%TYPE)
AS
  class_number_var class.class_number%TYPE;
  --start_date_var class.start_date%TYPE;
  end_date_var     class.end_date%TYPE;

  BEGIN
    -- Creates the next ID
    SELECT class_number_seq.NEXTVAL
    INTO class_number_var
    FROM dual;

    IF end_date_param < start_date_param THEN
      SELECT end_date_param INTO end_date_var
      FROM class
      WHERE class_number_var = class.class_number;
      end_date_var := start_date_param + 14;
    ELSE
      end_date_var := end_date_param;
    END IF;

    INSERT INTO class (class_number, teacher_name, class_name, start_date, end_date,
                       class_category, topic, teacher_credential)
    VALUES (class_number_var, teacher_name_param, class_name_param, start_date_param, end_date_param,
            class_category_param, topic_param, teacher_credential_param);

    COMMIT;
  END;
/

CALL insert_class('Collin Hannah', 'Intro to psychology', 01-OCT-15, 01-SEP-15, 'Psychology', 'Intro Classes', 'BS psychology');

BEGIN
  insert_class('Collin Hannah', 'Intro to psychology', TO_DATE('01-OCT-15','DD-MON-YY'), TO_DATE('01-SEP-15','DD-MON-YY'), 'Psychology', 'Intro Classes', 'BS psychology');
END;

--OR

EXEC insert_class('Collin Hannah', 'Intro to psychology', TO_DATE('01-OCT-15','DD-MON-YY'), TO_DATE('01-SEP-15','DD-MON-YY'), 'Psychology', 'Intro Classes', 'BS psychology');

SQL> create or replace procedure p
  2  as
  3  begin
  4  null;
  5  end;
  6  /

Procedure created.

SQL> sho err
No errors.

SQL> CALL p;
CALL p
     *
ERROR at line 1:
ORA-06576: not a valid function or procedure name

SQL> EXEC p;

PL/SQL procedure successfully completed.

TO_DATE('01-OCT-2015', 'DD-MON-YYYY','NLS_DATE_LANGUAGE=ENGLISH')

DATE '2015-10-01'