I haven't watched his videos but the tools are slightly better than just a hex editor. You can start by "disassembling" which decodes the hex into the set of CPU instructions. Then you can use graphical tools like IDA or Ghidra. You work through chunks of assembly and start grouping sets of instructions together into things like functions and label them. You end up with a load of (possibly labelled) boxes connected together by lines. It can be a painstaking and difficult process but the tools do help you tackle it piece by piece.