Once you have a Developer Edition or sandbox organization, you may want to learn some of the core concepts of Apex. Because Apex is very similar to Java, you may recognize much of the functionality.
After reviewing the basics, you are ready to write your first Apex program—a very simple class, trigger, and unit test.
In addition, there is a more complex shipping invoice example that you can also walk through. This example illustrates many more features of the language.