Are you planning to make a C++ (powder.exe) or Lua (autorun.lua) mod? Because I know quite a bit about lua mods

1)Load autorun.lua (find it somewhere on forum)

2)Open Lua window that will appear near walls section

3)Go to "online" tab and download any mod that adds an element

4)Press "local" and then press "Script folder"

5)Open .lua file and look at code, learn

But as i know lua scripts in TPT is quite limited, so it will be hard (or just impossible) to do things that can easily be done using C++. If you need any help with lua or C++ TPT modding you can write me in my discord: EvilGenius#9015.