There's no simple "101 guide on how to update offsets".
To give a short breakdown on how to improve and learn on your own, here's a couple of steps.
1) Do you have any previous knowledge of programming? If not, learn. You might as well start with a language that allows you to manually manage memory and deal with pointers since you will require this knowledge later anyway. Go with C++. This tutorial from start to finish will get you started,
C++ Language - C++ Tutorials
2) Do you have any previous knowledge of assembly language? If not, learn. This will be useful when using IDA/Ghidra and breaking down the binary, or when using cheat engine. Have a look at
Assembly Programming Tutorial, you don't need to do everything, just enough to get comfortable with how basic instructions works, the rest can be learned with a reference manual.
3) Download cheat engine and follow the tutorial that comes with it and in general start looking up reverse engineering tutorials or crackme's (see
https://crackmes.one/ for examples), there's hundreds if not thousands on the internet and again, plenty of information about PoE in specific on ownedcore. Here's for example is a thread where the creator of GH discusses how to quickly update offsets during league start,
mmo...ry-league.html
4) Have a look at YouTube, this ties into the previous point about learning the basics. I recently stumbled upon
this video and I found that it did a good job at explaining the bare basics but again, I'd personally recommend doing the previous steps as having the knowledge will help you further down the line, this also ties into my next point.
5) It's not an easy process and there's not really a way to make a "101 hold my hand for dummies" guide and even if there was one, you'll still need to understand the information and how to use it.
Hope that helps.
BanditTech is the creator of the very helpful color based tool
WingmanReloaded and as we both use GH, we decided to collaborate. As for what fork/version to use, up to you.