Understanding the explain statement

Hi all,

Something I never have really understood is the explain statement. I
know that it shows the query execution plan, but how am I meant to
understand the output? For example could someone give me some pointers
as to what is happening below?

Unique (cost=10.25..10.47 rows=4 width=80)

-> Sort (cost=10.25..10.25 rows=44 width=80)

-> Nested Loop (cost=0.00..9.04 rows=44 width=80)

-> Index Scan using region_pkey on region
(cost=0.00..3.01 rows=1 width=32)

-> Index Scan using feature_the_geom_idx on feature
(cost=0.00..6.01 rows=1 width=48

)

Any pointers to some docs would be good.

Thanks,

Benjamin