Pixel Pie 3D is a huge icon pack with a new and different style. In order to use it you simply need a launcher on your phone as a new launcher.
Instructions from the app page:
-Open the Pixel Pie 3D application and inside it go to the menu that is in the upper left.
-Select set or apply.
-It will show you the launchers supported and in the first place the ones you have installed.
-Select the one of your preference and press accept.
-You do not have any installed launcher just select it and it will take you to the download link of it.
-You can also open your launcher and from there apply Pixel Pie 3D Icon Pack.