Udon

Udon is how to make code in VRChat worlds. It is a visual scripting language, which means it uses blocks and nodes rather than traditional lines of code.
UdonSharp
If you already know C# and would rather use it to write your Udon scripts using lines of code, you can use UdonSharp to do so.
Note that UdonSharp behaviors are not MonoBehaviors. Not all methods in Unity's MonoBehaviors are exposed in Udon, which limits what you can code.
VRChat Udon Tutorial Videos Playlist
Many people view coding as a daunting black box. As a programmer myself, I can assure you that a basic understanding of it’s principles is not as complex as some portray it. The best advice I can offer you is:
Take it slow, don’t try to learn everything at once
Don’t dabble or attempt to modify a piece of code until you know what it does
Go in with a logical mindset
The last one is paramount. Think about the exact logical steps a computer would have to accomplish to achieve a desired result. Then putting it together will mostly be a process of translating that logic into computer code.
Oh, and the 2 most important tips:
READ THE CONSOLE!!! and
WRITE COMMENTS!!!!!!!!!!!!!!!!!!!!!!!!!!
Unity runs on C#, so if you would like to start learning a programming language, C# would be a great place to start. As of writing Brackeys is creating a tutorial series on programming for Unity. HOW TO PROGRAM in C# YT playlist
Basics
Data types:
Boolean - true or false
Int - an integer
Float - a decimal
String - a collection of characters
Note that ints in C# are 32-bit, which means they have a limit of ~2.1 billion, positive or negative. Exceeding this limit will result in overflow, which will cause errors.
Alternatively you can use the community-developed UdonSharp. It will translate C# script into Udon Behavior. It is more reliable, and if you have basic coding experience I would recommend using it over Udon’s visual script.