SQL Constraints

I am fairly new at SQL and also new to this forum. So I don't know if this topic belongs here or not.

But anyways, I found this tutorial online. However, I am having trouble completing it. Can someone please help me?

Given the following table definitions:

CREATE TABLE USERS
(
USERID CHAR(5) PRIMARY KEY,
NAME VARCHAR(30),
RATING CHAR(1) CHECK (RATING IN (A, B,C,D)
)

CREATE TABLE ITEMS
(
ITEM_NO NUMBER PRIMARY KEY,
DESCRIPTION VARCHAR(50),
OFFERED_BY CHAR(5) REFERENCES USERS(USERID) ON UPDATE CASCADE ON DELETE CASCADE,
START_DATE DATETIME,
END_DATE DATETIME,
RESERVE_PRICE NUMBER
)

CREATE TABLE BIDS
(
USERID CHAR(5) REFERENCES USERS ON UPDATE CASCADE ON DELETE SET NULL,
ITEMNO NUMBER REFERENCES ITEMS(ITEM_NO) ON UPDATE CASCADE ON DELETE CASCADE,
BID NUMBER,
BID_DATE DATETIME,
PRIMARY KEY(USERID,ITEMNO,BID_DATE)
)

Directions: Indicate whether the statement is accepted or rejected; and if accepted indicate its effects. Evaluate each statement INDEPENDENTLY.

1) INSERT INTO ITEMS VALUES(1009, Red Bicycle,U01,1999-01-08, 1999-02-10, 30)
2) UPDATE ITEMS SET ITEMNO=1008 where ITEMNO=1001
3) DELETE FROM ITEMS WHERE ITEMNO=1005
4) INSERT INTO ITEMS VALUES(1010, Green Bicycle,U07,1999-01-08, 1999-02-10, 30)
5) UPDATE BIDS SET ITEMNO=1011 WHERE ITEMNO = 1001
6) DELETE FROM USERS WHERE USERID=U01
7) UPDATE ITEMS SET ITEMNO=1020 WHERE ITEMNO=1001
8) DELETE FROM BIDS WHERE BID > 1001


Thanks. I would greatly appreciate your help.