Newbie

First of all you need a stable base source.

I would recommend one of those:
(VisualStudio 17) v18 Files with Current Retail
(VisualStudio 17) Flyff Base source for starter V18 mixed 21
(VisualStudio 19) Clean v17 Files
(VisualStudio 19) Clean v15 Files

Try to setup everything first. Make a fresh compiling and then start adding or editing your codes.

If you open a Source code you have to look into the VersionCommon.h

looks like this:
https://prnt.sc/rd556m

for example:
From the Source you want to copy something:
You want to add __LOOKCHANGE into your own source.

You will have to use the search function in your VisualStudio. In the Drop-Down menu you have to choose "Full Project"
(Sorry don't know how it is spell in the English version but you need to search through the whole project.
Maybe look for some tutorials for Visual Studio in the internet.)

now you search for every "__LOOKCHANGE" until VisualStudio says, that you have reached the last document containing the Word "__LOOKCHANGE".
you have to look for the #ifdef __LOOKCHANGE and #endif, this shows you where the code has been added or edited.

now you have all the .cpp and .h files open in your VisualStudio Season.
open the same files at your source code on another VisualStudio Season.

minimize visualstudio.

The Source you want to implement the "Feature":

Now you have to open the new source with a new visual studio season.

Open the same .cpp or .h file and copy the code into it.

How to Copy
From: #ifdef ___LOOKCHANGE
THE CODE
to: #endif

Depending on the feature you are trying to copy, you will have to add or edit your resource folder.
Explaining everything would consume a lot of time, luckily there are a lot of quality posts here.

You have to start small and build up your knowledge.

A little side note:
You ask for help multiple times but never hit a thanks button. People spend their free time helping you, its all out of good heart.
It's not only about giving thanks to someone helping you but also telling other readers, that a post helped you with your question or problem.

Good Luck