It’s a simple provider hosted SharePoint app that will convert your SharePoint public facing site, or your publishing site to a responsive site.
Once you add the app to your SharePoint site it will copy some files (Master pages and page layouts) to the Master Page Gallery under a folder named Custom.
Note: Make sure that you don’t have a folder with the same name otherwise all the files with similar names within the custom folder will be overwritten.
In the below screenshot you can see the files copied to the custom folder
In addition to that the app will upload a new PublishingImageRenditions.xml file to the root folder of the Master Page Gallery.
The app will not only copy custom files to master page library but also will create some custom lists and pages in your SharePoint site.
In your website create new document library and name it QueryPropertiesTemplate, upload this xml file to it.
Go to your website update the page library versioning settings to allow checkout before edit
Add the app to your site and wait for the app to be successfully added and all the related SharePoint artifacts are created.
for more information please check this blog post