Code is instructions written in a programming language. It tells a computer what to do, step by step. A line of code might add two numbers, display a message, or send data to a server. Thousands of lines together form a program. Millions form an operating system.

Code is not magic. It is text. You can read it, edit it, and break it. The computer does exactly what you write, not what you meant. That is why debugging takes so long. A missing semicolon can crash a whole application.

Levels of code

• Machine code: binary instructions the CPU executes
• Assembly: low-level mnemonics, close to hardware
• High-level: Python, Java, C++, readable by humans
• Markup: HTML, XML, describes structure not logic

Good code is readable. Bad code works but confuses everyone who touches it later. Teams adopt style guides, code reviews, and automated tests to keep quality up. Writing code is easy. Writing code that others can maintain is hard.