The UWP Tile Generator gives you the ability to generate the tiles required to submit a UWP to the Universal Store. A simple right-click on an image in your project and this VSIX takes care of the rest. As well as generating the images it also updates the package manifest.
Rather than write a lengthy blog post, have a look at one I wrote earlier: https://blogs.windows.com/buildingapps/2016/02/15/uwp-tile-generator-extension-for-visual-studio/
To download the extension please go here: https://visualstudiogallery.msdn.microsoft.com/09611e90-f3e8-44b7-9c83-18dba8275bb2
and if you would like to contribute and add more features to the UWP Tile Generator then don't be shy! Head over to: https://github.com/shenchauhan/UWPTileGenerator
and create a pull request.
Hope this helps you in your UWP apps.