Reddit mentions of Handbook of Relational Database Design

Handbook of Relational Database Design by Fleming and von Halle

I found the best way to think about relational data in general is to start with an old book, one that covers the subject in a pure way without reference to any particular system. Then you can translate the concepts into a nice modern system like PostgreSQL. http://www.amazon.com/Handbook-Relational-Database-Candace-Fleming/dp/0201114348

If you just want to jump in and try stuff out here are some tutorials and docs.

Here are some tutorials about triggers
http://www.postgresqltutorial.com/postgresql-triggers/

Managing roles (the "official" docs are actually pretty good)
http://www.postgresql.org/docs/9.4/static/user-manag.html
http://www.postgresql.org/docs/9.4/static/sql-grant.html
http://www.postgresqltutorial.com/postgresql-roles/

Creating schemas and using the search path
http://www.postgresql.org/docs/9.4/static/ddl-schemas.html