How to learn Postgres?

Hello
I've installed Postgres last week and I plan to learn this database.

I've been using Access and other databases such as dBase (a long time
ago), for more than 10 years, but I don't know how to project my
knowdledge to Postgres.

Does anybodu has the same problem?
Does any know any document, book or url where find some information
about how to learn the psql concepts from another database system?

Thanks in advance (and excuse my english).

--
In a world without walls and fences, who needs windows and gates?