Code documentation is the process of adding comments, annotations, and descriptions to your source code. This is done to explain what it does, how it works, and why it is written that way. It can be divided into two types: inline and external. Inline documentation is written inside the code files, using a syntax or format that depends on the programming language. For example, in Python, triple quotes (""") are used to write docstrings. This type of documentation is useful for providing immediate and contextual information about the code, but it can also make it less readable. External documentation is written outside the code files, using a separate tool or platform that generates a structured and formatted document. Tools such as Doxygen, Sphinx, or Javadoc can be used to create HTML pages that display comments and references. This type of documentation is useful for providing an overview of the code but must be updated regularly to remain accurate. To document your code effectively, it's important to choose a style and tool that suits your language, project scope, and audience. Write clear and concise comments that explain what, how, and why of your code. Use consistent naming conventions for variables, functions, classes, and modules following standards of your language or framework. Document your code as you write it to avoid missing out on important information. Finally, review and update your documentation regularly to make sure it reflects the current state of your code.