Imagine you are playing hide and seek with your friends. You hide behind a tree and wait for your friend to find you. Your friend calls out your name and you have to respond by saying "Here!" This is just like how applications work. You tell an application what you want it to do, and the application responds by doing it for you.
Application response measurement is like timing how fast you and your friend respond to each other in the hide and seek game. When you tell an application what to do, you want it to respond quickly and do what you asked it to do. To make sure the application is responding fast enough, developers use tools to measure how long it takes for the application to respond to your request.
This measurement is important because if an application takes too long to respond, it can be frustrating to use. Just like waiting a long time for your friend to find you in the game can be boring and annoying. By measuring the application response time, developers can find ways to make the application faster and more enjoyable to use.