Stage Selection UI Sizing
It consists of 20 stages, from the easiest single vowel to the most difficult one.
It was logically designed so that you can remember character of the before stage without having to review it. Were you envious of your friends who can read Hangul? You can do it, too. And you can quickly distinguish many similar letters.
If you have given up learning Hangul, try again (Learn Hangul).
You will be able to write and read Korean, which you could only speak.