Understanding Schema's

I've recently switched from MySQL & have read the documentation for
'schema's' however I guess I'm just not at that level or really daft
when it comes to database design.

http://www.postgresql.org/docs/current/static/ddl-schemas.html

I'm trying to understand the relation between actual databases &
tables but can't grasp the relation with schema's so I was wondering
if someone has an easy way of explaining this beyond the documentation
I linked above. I notice my fresh 9.0 install has a default schema
called 'public' which every newly database I create defaults to and I
also created two new schema's called 'fire' & 'ice' but from what I
have written above, obviously I don't have any understanding of how
they work.

I greatly appreciate any info and or help since I appear to be lost.

-Carlos