What is the Lock&Korean: Learn Korean words on the lock screen application, how does it work?

According to the introduction of Boreumdal Lab., Lock&Korean: Learn Korean words on the lock screen is a Education app on the Android platform. There is currently a 3.8.10 version released on Mar 25, 2020, you can see the details below.

Lock&Korean is the best free app for learning Korean.
It contains more than 2300 common Korean words and phrases with excellent audio.
All contents are maded by native speakers.

[ Features ]
- All contents are free
- Over 2300 commonly used words and phrases
- Many tests: Listening, Speaking, Writing, Sentence Completion etc.
- All contents are made by native Koreans.
- Simple user interface

[ Courses ]
- Korean Alphabet: consonants, vowels
- Basic Words series
- Essential Adjectives
- Numbers, Calendar, Time
- Food, Dish
- Reading Korean ...