Here are five easy words/phrases that you can learn from this song. Check the subtitles for more vocabulary :)
사실은 (sa-shil-eun) - honestly
공부하다 (kong-bu-ha-da) - to study
잘 들어 (jal deu-reo) - listen well!
위선자 (we-seon-ja) - hypocrite
물어봐 (mul-eo-bwa) - try to ask
If you have any more questions feel free to ask me!