Trying to join sales numbers - having trouble

Question

I'm very new to Sql. I'm trying to join two queries into one. They each work independently, but when I try to combine them I get duplication - the same part is listed numerous times. I know it's something simple, but I can't figure it out. Any help would be much appreciate.
Query #1 - Pulls sales for last 30 days*
(select sitecode, physical_warehouse, partno, sum(qty_used) as qty_used_1_month
from partsusage
where ((date_usage > add_months(trunc(sysdate), -1))
and (date_usage <= trunc(sysdate)))
group by sitecode, physical_warehouse, partno) SOLD
Query #2 - Lists the site, part #, and order type._
SELECT ORDER_PARTS.SITECODE_SUPPLIER as orig_sitecode_ship_from
, order_parts.partno
,order_header.order_sub_type,
FROM ORDER_HEADER, ORDER_PARTS
Queries combined:*
SELECT ORDER_PARTS.SITECODE_SUPPLIER as orig_sitecode_ship_from
, order_parts.partno
,order_header.order_sub_type,
FROM ORDER_HEADER, ORDER_PARTS
, (select sitecode, physical_warehouse, partno, sum(qty_used) as qty_used_1_month
from partsusage
where ((date_usage > add_months(trunc(sysdate), -1))
and (date_usage <= trunc(sysdate)))
group by sitecode, physical_warehouse, partno) SOLD

Answer 1

Looks like a lovely Cartesian join to me ... your WHERE clause contains filters but no joins.
Run the demos here:
http://www.morganslibrary.org/library.html
under joins and bookmark the library page for future reference.