Understanding APIs in Modern Software

APIs are the rules and interfaces that let software systems communicate in a predictable way. In this lesson, learners will build a clear mental model of what APIs are, how they differ from web services, and why they are essential to modern applications.

The lesson focuses on practical foundations: common API use cases, key terms such as requests, responses, endpoints, and payloads, and the basic flow of how one application asks another for data or actions. It also introduces the client-server relationship and explains why APIs make software more modular, scalable, and easier to integrate.

By the end of this lesson, learners should be able to recognize an API in real-world products, describe how an API call works at a high level, and identify the role APIs play in mobile apps, websites, and backend systems.