So first thing is, you’ll need to download the game. If you’re in Japan, all good! If not, you’ll need to find the APK or use QooApp which is a Chinese app that lets you download region locked apps.
As for iOS, you’ll need a Japanese account to get the game. Please google on how to make a Japanese iTunes account as there’s plenty of guides out there. Steparu’s method might be a way.

Once you start, the game will guide you through a tutorial, pay attention!
After that, feel free to browse the menu items at the top to see what the moonrunes say.