Can anyone explain how this works?

Hi,

I recently posted this same question a few weeks back but lost the reply
someone kindly sent. The question again how exactly does this query work:

it will return all attributes and respective data types of a given table':

select attname, typname
from pg_class c, pg_attribute a, pg_type t
where relname = relation_name and
attrelid = c.oid and
atttypid = t.oid and
attnum > 0
order by attnum;

Many thanks,

Rob Burne.