Easy Quick Steps to Publish Unity Games to Windows Store
Once you've created the Build in Unity, you'll need to open up the .sln solution file in visual studio.
Make sure your build configuration options are set to Master and x86 otherwise you'll get failed API Errors during the certification test.
Then just follow the steps in this video by Microsoft, it's only 2 minutes. https://channel9.msdn.com/Blogs/One-Dev-Minute/How-to-publish-your-Unity-game-as-a-UWP-app