Hello [name]! Thanks for joining the GMC. Before making any posts in the Tech Support forum, can we suggest you read the forum rules? These are simple guidelines that we ask you to follow so that you can get the best help possible for your issue.
You're right that extensions are needed. Take a look at YYG's help articles; I had found them quite helpful. Sometimes you'll also need domain knowledge about android development, which should be available on developers.google.com. The Google Play Services Extension should also be an okay example to look into; the marketplace also has abundant examples.