Starting from a single switch, by directly building devices that process calculations, memory, and commands one by one, you will gain a deep understanding of how the computers we use every day are constructed. Recommended for those who desire an integrated experience connecting core concepts of computer science. This lecture is the Korean version of the world-renowned Nand2Tetris course, structured with the original author's permission and request. Keywords: Nand, HDL, ALU, PC, RAM, CPU