I got an S7 edge a few weeks back and was excited about the external SD CARD support. Unfortunately it's still not integrated very well. You still have to go in and manually set it all up. Apparently Android Marshmallow has support for creating a seamless file system across internal and external storage.
The easy way
This is I guess how they wanted you to manage this stuff
Here is an app that can't be moved. Anything that came pre installed on the phone appears to be pinned to internal storage.
Here the Messenger app can be moved
Tap the change button then you'll be presented with this option.
Confirm you want to move the app
Transfer in progress screen
Back on the messenger application screen you can see that it's now on external storage
Android Ninja way
With ADB apparently there is a way to enable the native android file system spanning in Marshmallow (my non standard term for it) that will be another write up.