In its Android Nougat change log, Samsung notes that "some Apps that haven't been optimised for Android Nougat might not work properly after the upgrade." In this case, it says, "upgrade to the latest version via Galaxy Apps or Play Store."
If you rely on various apps to get through your day, this is going to be extremely important and now would be a good time to check the Galaxy Apps store and the Google Play Store for Nougat support updates. They will help.
Developers, Samsung included, will be rolling out updates that will help make your transition from Marshmallow to Nougat as smooth as possible. However, it's on you to take the time to find and download these updates.
We should see a number of updates trickle out over the next few months so make sure you keep your eyes peeled for them.