Code
also: source code
The written instructions that make up software. It is text, written in a strict language a computer can follow, such as Python or JavaScript.
Human-readable text written in a programming language that describes what a program should do. It is either run directly by another program called an interpreter, or first translated into a form the machine can execute.
Code is like a recipe written in very strict language. The kitchen follows it word for word, so a missing step or a typo changes what comes out of the oven.
Your agent reads and writes code for you. You don't have to write it yourself, but knowing it is just text you can open, read and ask about keeps you in charge of your project.
I've added the code for the discount field. It checks that the coupon exists before applying it to the cart total.
Before you change any code, explain in plain English what the current code for the sign-up form does.
Thinking code is something only programmers can read. Much of it uses English words, and you can always ask your agent to walk you through any piece of it.