The tutorial covers most of the important concepts of OSGI. The only drawback is the example that is given in this article. The example uses MANIFEST.MF configuration file to define meta information. Though project works fine with manifest file there are some disadvantages using it.

To know more information about using pom.xml over MANIFEST.MF file, I recommend to go through this link:https://stackoverflow.com/questions/11373009/should-i-use-pom-first-or-manifest-first-when-developing-osgi-application-with-m

Overall, I highly recommend this article to anyone who want to know about OSGI in-depth and it is completely fine if you are unable to follow the example.
If you want to do hands on project using OSGI, go through the below mentioned link. The best thing about this example is it uses MAVEN build tool and IntelliJ IDE. The more things about this article will be covered in next part of this series.

https://medium.com/javarevisited/learn-osgi-from-scratch-eclipse-intellij-and-wso2-platform-%EF%B8%8F-bf4c5629e097

The pom first versus manifest first is interesting. My understanding of IGB is that we are very pom first. There are some interesting points made in the stackoverflow, I always try to pay attention to what Neil Bartlett says. This comment by Christian Schneider also caught my eye:

For server side OSGi projects I favour the pom first style. It nicely matches the maven builds and is much less error prone than Manifest first. In fact bnd which is behind the maven bundle plugin gets the Manifest right for most cases without any additional config. The trick is to use some naming rules. For example if you name internal package impl or internal the will not be exported.