Joining more than 2 tables

Hi,
    I am trying to join 3 tables
with this query
    select a.id, a.name, sum(b.qty), sum(c.qty)
    from a, b, c
    where a.id=xxx and b.id=a.id and c.id=a.id

what the sums that get returned look as if they are a cross products of
the b and c tables.

What is the correct way to join these tables?
Pointers to docs is welcome

Thanks
Jeff Meeks
jmeekssr@net-serv.com