How does two application communicate with each other ?

When two applications need to communicate with each other, they typically use something called an Application Programming Interface, or API.

An API is a set of rules and protocols that defines how two applications can talk to each other.

One application will send a message, or request, to the other application through the API. The other application will then receive this message and send back a response, all through the API.

To give you an example, let's say you have a weather app on your phone. This app gets its data from a weather service API. When you open the app, it sends a message to the weather service API asking for the current weather conditions in your location. The weather service API then sends back a response to your weather app with the current weather information. Your weather app then uses this information to display the weather on your phone.

Weather App <-> Weather Service API

Behind the scenes, the weather app and the weather service API are communicating with each other using a common language and a set of rules defined by the API. This allows the two applications to work together seamlessly, even though they were created by different developers and run on different platforms.

And that's how two applications communicate with each other using an API! It's like two people speaking a common language and following a set of rules so they can understand each other and work together.