An app is short for application, which is a software program. Apps can help people play games, read the news or find their way. You may tap on one without a second thought. Here is a question to start with: what is really going on when you do? Let's look at it one part at a time.

Start at the bottom, with the operating system. An operating system is the main software that manages a computer's resources and lets other programs run. It manages resources such as memory, the processor and devices for the programs running on a computer. Android and iOS are two operating systems for phones. Let's look at what that means for the programs you use. It may be easier to see than you think, and it starts with one simple idea. Read each part and picture it in your mind before you go on, because the next part builds on it.

On Android, an app is packaged in an APK file, and Android devices use that file to install the app. An Android app, by default, runs in its own process, and the system starts that process when one of the app's parts needs to run. Let's look at how that works on one kind of phone, and take it slowly, step by step, so that each part makes sense before we move on to the next one, and so that you can see what goes on inside.

Here is a piece of web code. JavaScript is a scripting language that makes web content update on its own, and it is the third layer after HTML and CSS. In web code, an event such as a click can run code, for example code that changes a label. Think of the last time you pressed a button on a page. Some code was waiting for it, and the page answered. Let's keep that picture in mind as we go.

Many apps also depend on a computer far away, one that you will probably never see or touch. Here is how they talk. It helps to take it one piece at a time and to picture each piece as you read, so go slowly. A server is a computer on a network that stores things like files and sends them to other devices. Network-connected apps often use HTTP to send and receive data, and a server answers each request with a response. A database is a repository of information that a server can pull content from to build a page or screen.

Now think about the people who build apps, and that is where the story of an app begins. Let's meet them, and see what they use to do their work, from start to finish. Apps are made by developers, who may work alone or in a team. Computer programs are written in programming languages such as C, Python and C++. A program is first written in a computer language by a person and then translated into a form the computer can run. Developers use special tools to build and fix apps, such as Android Studio and Xcode. As of November 2026, Apple lets developers test early versions with up to 10,000 outside testers through TestFlight.

How do apps reach people? Here are some dates and numbers to chew on. Apple opened its App Store in 2008, and people get apps from an online app store. More than 100 million apps were downloaded in the first 60 days after Apple opened its App Store in 2008, and by January 2010 more than three billion had been downloaded. As of November 2026, Apple reviews apps before they appear on its App Store. Apple says apps that cheat the review system can be removed and the developer expelled from its developer program. Apple handles payments and hosting for apps in its App Store, so developers do not have to build their own store.

Here is a question that matters to anyone who builds things for a living, and to anyone who has ever wondered who pays for what is on a phone. How can they earn a living? Developers can earn money from an app by charging for the download or for features inside it, as of November 2026. In-app purchases let a person pay for extra things inside an app. Some apps offer auto-renewable subscriptions, which the App Store has supported since 2011. You may have seen a price like that on a screen, and now you know what to call it.

What does an app get to see? This is a big question for anyone who carries a phone. Apps may ask for permission to use information on a device, such as contacts, calendar entries and location. A phone's settings let a person change an app's permissions after they first answered. Some apps share information from a phone with other companies that show ads based on a person's location and interests. As of November 2026, a person can tell an app on iPhone not to track them and still use the app's full features. On Apple's App Store, each app has a privacy label meant to help people understand what data the app collects and how it is used.

Here are some words about updates and scams. They are good words to know. Updating an app gives you the latest features and makes it more secure. Many software updates are made to fix security risks. Malware is software made on purpose to cause harm. Phishing is when criminals try to get people to open harmful links or attachments, and it can come as an email, text, direct message or phone call.

Ask a grown-up before you get an app. Parents can set up a phone so that a child has to ask a grown-up before getting an app. Some phones have settings that let a parent make a child ask permission before downloading or buying apps. The COPPA rule was designed to protect children under age 13. As of November 2026, Apple's Ask to Buy is turned on by default for children under 13. When a child asks to get an app on an iPhone, the parent can approve or decline the request from the parent's own device.

Words to know

• developers: app makers
• JavaScript: web scripting language
• database: stored information
• phishing: tricking people
• malware: harmful software