In the first part, you build the building blocks of a computer(logic gates, ALU, cpu, etc) using a hardware coding language on a software program. You’re not assembling components like power supplies, hard drive, graphic cards when building a PC if that’s what you were thinking. It’s low level. The second part is when you build the software layer, like a compiler, a VM, a simple OS, and then finally you develop a game like Tetris that you can run on the computer you just built. Here are the links for both parts.