I'll take a stab at a newb-friendly explanation, bearing in mind I'm only slightly less of a newb, but have at least studied this stuff to some extent and have

I'll take a stab at a newb-friendly explanation, bearing in mind I'm only slightly less of a newb, but have at least studied this stuff to some extent and have played with https://microcorruption.com https://microcorruption.com, which is a game about maliciously editing machine instructions. Onwards! CPUs have a fixed instruction set. Add, subtract, increment by 1, and so on. These instructions in turn are represented in machine language as a binary string, which represents signals that get sent to the CPU's processing center, the ALU (Arithmetic Logic Unit). The ALU has a number of input ports, with each one corresponding to a different fundamental operation. There are a number of programs capable of taking an executable and providing a step-by-step breakdown in machine language (which makes sense intuitively because the machine has to do this for itself anyway in order to execute the program). So once you have the machine language instructions, you then study it to see what different sets of instructions are doing. This is made somewhat easier by the fact that computers run through instructions linearly (with the exception of jumps, but you also know that jumps represent some sort of logic operating on input, so those are informative as well). Although this would take forever to do manually, there are programs that aid in breaking machine language into easier-to-understand chunks, like IDA. Anyway, once you understand what different chunks of instructions are doing, then you can decide how you want to alter the program. You can use a hex editor for the actual editing (I assume professionals use something different, but some game modders use hex editors), which simply lets you change the individual bits on your drive (if this sounds impressive, realize that every time you save a file or something, that's what's going on at a large scale). If you want a gentle, newbie-friendly introduction to CPUs which will make a lot of this stuff click better, I highly recommend the NAND to Tetris course, which has a video series on Coursera: https://www.coursera.org/learn/build-a-computer https://www.coursera.org/learn/build-a-computer