One of the best things I ever did was learn how to make an instruction decoder. Logic gates were easy enough, and flip-flops made sense; it's easy to see how to use flip-flop gates plus a clock signal to make a clocked computer, but getting all the way to instruction decoder made it all come together. I forgot the actual game that taught me, some zach-like (but not actually a zachtronics game) on steam. Still, it really means it all click.