It's two things that are not explained in the game. Locking I only know exists because of the About The Game section. But there's 0 explanation on how to do it. Furthermore I don't know how the scoring works. It's always just a number showing up that I don't know of how it has been calculated. Also, what decides the multiplier....

FYI, according to your (English) store page, English is not supported for your game, only Japanese and Chinese.