Eclipse e4 right now is almost the synonym of the word "future".
If you look for an excellent presentation that will bring you into the future, you can find it here (made by Tom Schindl).
Reading JSR 330 is also a good idea, because it will give you the basic understanding of Dependency Injection.
The last, but not least, is looking at org.eclipse.e4.core.services.context.IEclipseContext javadoc, and then, in the end, at org.eclipse.e4.workbench.ui.internal.Workbench.
All those readings will give you fair understanding of how dependency injection is used in e4.