During the course of this book, we will use custom packages, since we don't have time to create all the graphics on our own.
For our first game, we are going to use a package from http://kenney.nl, which is a website full of interesting graphic packages, and free to use in any project. In particular, you need to download the following package: http://kenney.nl/assets/platformer-art-deluxe.
Once the file has been downloaded, it is compressed, so we will need to open it with a software for decompression.
As you can see, there are many folders containing different expansions of the pack. We only need the basepack folder. We need to copy this folder into the Asset folder in Unity. You can do this by just dragging and dropping it in the Project panel. Finally, we can rename it PlatformerPack, so our project will be better organized.