Monthly Bill Problem

Hello All, I need calculate all item?s cost for a particular month to produce monthly bill.
Could you help me please.

COLUMN surname NOPRINT NEW_VALUE sname
COLUMN today NOPRINT NEW_VALUE to_day
BREAK ON surname SKIP 2
COMPUTE sum OF COST ON surname
TTITLE CENTER ‘Monthly Bill’ SKIP –
LEFT ‘Name: ‘sname ‘ RIGHT ‘Billing Date: ‘to_day SKIP 2
SELECT TO_CHAR(SYSDATE,’DD/MM/YY’) today, surname, item_desc, chargedate, item_cost
FROM order
WHERE cust_id = &&cust_id;