I was seeking for test frameworks for Android UI automation and I stumbled upon UI Automator and Espresso and this is the part I am confused about
I've found an interesting article, which talks about why you should use them both. Take a look at:
http://qathread.blogspot.com/2015/05/espresso-uiautomator-perfect-tandem.html
Already Espresso is enough for me, but for some reasons like testing app notifications I would in just a few weeks learn uiautomator.
Spend some time to
https://github.com/googlesamples/android-testing/tree/master/ui
http://developer.android.com/training/testing/ui-testing/espresso-testing.html
http://developer.android.com/training/testing/ui-testing/uiautomator-testing.html