You don’t need to know Japanese to use it
Don’t touch the die button
The green button is for when you are done
Then there are the tabs for editing, in the picrew I linked the first tab has the outline of a body.
You can click the paintbrush to change the color of the accessory, or in this case skin color
The next tab on this picrew (with the eye on it) controls the eyes. It has different eye outlines for you to pick from, and you can change the color with the paintbrush
If you click the arrows above the four pink squares, you can also change where the eyes are