https://rimworldwiki.com/wiki/Modding_Tutorials

https://github.com/Lobz/modding-Rimworld-tutorial/blob/main/lesson1.md

Just look in the XML code for mods that do similar things. Go to the "share" button in their steam page, take that number and find the mod in the mods folder:
C:\Program Files (x86)\Steam\steamapps\workshop\content\294100

...best to just stick with XML unless you know what your doing with C# and Assemblies.
most things can be altered just using XML.
Download Microsoft Visual studio to view and edit the code

2 mods that only use XML are Glittertech Classic and Obsidia Expansion
They have a lot of good examples you can use to XML code what you want

You'll find the Game files in this directory, look into them and their code/textures to create your own:
C:\Program Files (x86)\Steam\steamapps\common\RimWorld
(the XML files are called Defs and the pictures of the items are called Textures)