I'd start here: http://www.postgresql.org/docs/9.3/static/index.html

I've always found this documentation to be great.

If you've worked with RDBMS' before, you can skip around the chapters. If not, I'd read up through chapter 14 and go from there.

You should be able to easily install it on whatever OS you're running.

The Schemaverse (http://schemaverse.com)

Play a space battle MMO, but using SQL. The game is also completely open source so if you want to find out how to write an entire application layer in PostgreSQL, it is a pretty good example of that.

This is a shameless plug, but hopefully all some good resources:

  http://www.craigkerstiens.com/categories/postgres/ 
  http://postgresguide.com/
  http://www.postgresweekly.com