Insert the micro SD card into your Raspberry Pi and start it up.
Unlike cgwg's, though, the Gameboy shader also uses some lookup textures (LUT) that require no text editing and can be modified using an image editor such as Photoshop or GIMP. RetroPie has tons of emulators for different consoles built right in.
RetroPie: Enable Video Shaders and Add Video Shader Hotkeys This post will go over how to enable shaders and set up hotkeys so that you can change shaders while playing games.
