To get the best experience in Narrative, it's best to be upgraded to the latest version of macOS, the current version is macOS High Sierra which Narrative is optimised for.
To upgrade to macOS High Sierra go to the Mac App Store and search for High Sierra.
For more information see this article by Apple
How to upgrade to High Sierra
To check which version you are currently on:
- Click the Apple menu.
- Click About This Mac.
Make sure your Mac is compatible by checking here.