Users download the app to their devices, and can then browse and download any number of Microsoft apps. That's it. There's no special sauce or exclusive content that users can only get through Microsoft Apps (at this point), just a simple, straightforward directory of all the Android applications available from the company.
What's somewhat remarkable about all this is that it shows Microsoft's growing support of and commitment to Android as a platform. The company actually has enough apps available for Google's OS that it doesn't feel like a ghost town, which is a far cry from where things were a few years ago.
On its own, this seems like a bit of an odd move. Users who want to find Microsoft's apps in the Google Play Store can just look through the company's whole listing inside Google's app store, without having to download Microsoft's dedicated directory.
It's also possible that the app may be helpful to IT managers who want to direct their users to approved applications, or to people who don't want to deal with Google Play, but that seems like a fairly limited use case for creating such an application in the first place.
The app's description teases that there's "more coming soon" to Microsoft Apps, so we may see it become something else in the future, like an alternative to distributing apps from sources other than Microsoft. For right now, though, it's a fairly limited tool.