Many command line applications enhance usability and organization by using subcommands, which group related features under distinct command structures—examples include Docker, Git, and GitHub CLI. Subcommands clarify how to interact with CLI tools by separating actions (like adding, subtracting, or managing resources) into logical, discoverable operations. Building subcommands from scratch in Go, without third-party libraries such as Cobra, helps deepen understanding of core command line argument handling—primarily by parsing arguments, validating input, and routing execution using basic constructs like switch statements and handler functions. For illustration, a basic calculator CLI can implement subcommands for addition and subtraction, with each command acting as a focused, testable subroutine, and robust error handling for invalid input. This approach not only leads to more user-friendly and extendable tools but also provides a solid foundation for implementing similar features in other programming languages. Future lessons further enhance functionality by introducing command line flags and custom abstractions for even more powerful and maintainable CLIs.