Typically, one starts out with these things stepping through the installation process and account creation. Installing PostgreSQL can be very easy with one click installers or can be far more involved depending on the level of complexity, customization and control that one requires. (In the examples here I installed PostgreSQL 9.0.1 from source code on OSX in about 10 minutes, much of which was waiting for the code to compile.)
I'm going to assume that you are a novice and that the IT guy, the database administrator, or a friend has installed PostgreSQL successfully and created you an account. (If enough people complain I can write a post on installation but for now let proceed straight to using it.)
You have a PostgreSQL account with a username and a password. Let's get to it.