If you're a beginner with OSGI I wouldn't start by mucking around with as complex an application as Eclipse. Start with a simple example instead that doesn't have any other external dependencies. The Felix examples I pointed you to accomplish that nicely.
I have did the following steps
1. create Activator.java file
2. generate the jar file "BundleExample1.jar"
3. start it using the command
start file:/home/test/Desktop/BundleExample1.jar