This article illustrates the basics of a developer account.
Understanding the Force.com Platform vs. the Advologix Practice Management application

The Force.com Platform
The first concept you must understand is that Advologix is part of a larger technical platform called Force.com. This platform-as-a-service is provided by Salesforce.
One way to easily understand it is to think of the Force.com platform like Windows or Mac OSX and AdvologixPM is like a practice management application that is installed on those platforms. As a result, in addition to learning the Advologix Practice Management application, there are many areas for learning and understanding NEW concepts within the Force.com platform. Think of it as installing Windows for the first time and having to learn how to set up your desktop, the Start Bar, all the options in Control Panel and all the Accessory applications that come with Windows out of the box. The SAME concept applies here with the Force.com platform.
Now that you have signed up for your free developer account, you also have access to all the resources at http://developer.salesforce.com and you can log in with the username and password you used to set up and access your system.
We suggest starting at the following links:
Follow the tutorials in the Force.com Workbook
Download and read the Force.com Fundamentals Book
Starting learning more with other Getting Started Material