A computer app is a program you run on your device to do a specific task

An app (short for process) is software designed to perform one job or a small group of related jobs. Unlike your operating system—which runs your entire computer or phone—an app does something concrete: edit photos, send messages, play music, track your budget, or browse the web. You launch it, use it, and close it when you're done.

Apps exist on phones, tablets, and computers. On your phone, you tap an icon to open one. On a computer, you might double-click a desktop icon or search for it in your start menu. The app runs in its own window or full screen, separate from other programs you have open.

The key difference between an app and the operating system is purpose. Your operating system (Windows, macOS, iOS, Android) manages your hardware—the screen, keyboard, storage, memory—and lets different programs share those resources. An app uses those resources to do something you actually want: write a document, watch a video, or check your email.

Key Takeaways

  • An app is a program that performs a specific task, like messaging, photo editing, or banking, and runs separately from your operating system.
  • Apps are installed on your device and launched by clicking or tapping an icon; they use your device's hardware (screen, keyboard, storage) to function.
  • Mobile apps (on phones and tablets) and desktop apps (on computers) work the same way but are built differently depending on the operating system.
  • Most apps are free or cost a small amount, and you read them from official stores like the App Store, Google Play, or Microsoft Store.

How apps are built and where they come from

Apps are written by programmers using code—sets of instructions that tell your device what to do. A programmer writes the code, tests it to make sure it works, and then packages it so your device can understand and run it. Different operating systems need different code, which is why an app for iPhone doesn't automatically work on Android, and a Windows program doesn't run on a Mac without modification.

You get apps from official stores. On an iPhone, that's the Apple App Store. On Android phones, it's Google Play. On Windows computers, it's the Microsoft Store (though many Windows apps are also downloaded directly from company websites). These stores check apps before listing them—not perfectly, but enough to filter out obvious malware and scams.

Some apps are free. Others cost money, usually between $0.99 and $9.99 for one-time purchase, though some charge a monthly or yearly subscription. Free apps often show advertisements or offer a limited version with the option to pay for more features.

The difference between web apps and installed apps

Not all apps are installed on your device. A web app runs inside your browser—Chrome, Safari, Firefox, or Edge—and lives on a company's server instead of your computer. Gmail, Google Docs, and Canva are web apps. You don't read them; you visit a website and use them there. They work on any device with a browser, so you don't need a separate version for iPhone, Android, or Windows.

An installed app (also called a native app) lives on your device itself. It's faster because it doesn't need to send information back and forth to a server as much. It can also work offline—you can write in a notes app or play a game even without internet. But you have to read it first, and it takes up storage space on your device.

Many companies now offer both. Microsoft Office, for example, has an installed version you buy and read, and also a web version (Office 365) you use in your browser. The choice depends on what you need: web apps are convenient and work everywhere; installed apps are usually faster and work without internet.

What happens when you open an app

When you click or tap an app icon, your operating system finds the app's files on your device and loads them into your device's memory (RAM). The app then draws its interface—buttons, text boxes, images—on your screen. It waits for you to interact with it: type something, tap a button, or drag an image.

Each action you take sends a signal to the app's code. The code processes that signal, does whatever calculation or task is needed, and updates what you see on screen. If you're editing a photo, the app loads the image file, applies the filter you selected, and shows you the result. If you're messaging a friend, the app takes your text, sends it to a server, and displays your friend's reply when it arrives.

When you close the app, it stops running and frees up your device's memory. Some apps save your work automatically; others ask you to save before closing. If you force-close an app without saving, you lose unsaved changes—the same as closing a document on a computer without saving it.

Common types of apps and what they do

Apps fall into broad categories based on their purpose. Productivity apps help you work: word processors, spreadsheets, note-taking tools, and calendar apps. Communication apps let you message, email, or video call: WhatsApp, Slack, Outlook. Media apps play music, video, or podcasts: Spotify, YouTube, Apple Music.

Social media apps connect you with other people: Facebook, Instagram, TikTok. Utility apps do small, practical tasks: flashlight, calculator, weather, timer. Gaming apps are games you play on your device. Shopping apps let you browse and buy from stores: Amazon, eBay, Target. Banking apps let you check accounts and transfer money from your bank.

Most people use a mix of these. You might have a messaging app, a banking app, a maps app for directions, a music app, and a few games. You don't need to use every app available—only the ones that do something you actually want to do.

How much storage and memory apps use

Every app takes up storage space on your device. A small utility app might use 5 to 10 megabytes (MB). A large game or photo editor can use 500 MB to several gigabytes (GB). If your device is running low on storage, you can delete apps you don't use to free up space. Uninstalling an app removes it completely and recovers that storage.

Apps also use memory (RAM) while they're running. A straightforward app uses 50 to 100 MB of RAM. A complex app like a video editor or game can use 500 MB or more. If you have too many apps open at once, your device slows down because it runs out of available memory. Closing apps you're not using speeds things back up.

Updates also matter. App developers regularly release updates that fix bugs, add features, or improve security. Updates can make an app larger. If an app suddenly uses much more storage after an update and your device is nearly full, you may need to delete other apps or files to make room.

How to keep apps safe and working well

Keep your apps updated. Developers release updates to patch security holes and fix problems. On most devices, you can set apps to update automatically so you don't have to remember. Check your app store's settings to turn on automatic updates.

Only read apps from official stores—the App Store, Google Play, or Microsoft Store. Apps from unknown sources are more likely to contain malware or steal your information. If an app asks for permissions that seem odd (like why would a flashlight app need access to your contacts?), that's a warning sign.

Delete apps you don't use. They take up storage, can slow your device, and may collect data about you even when you're not using them. If you think you might use an app again later, you can always read it again—your data is usually saved in the cloud.

Frequently Asked Questions

What's the difference between an app and a program?

The terms are often used interchangeably, but "program" is the older, broader term for any software. "App" usually refers to smaller, single-purpose programs, especially on phones and tablets. A word processor on a computer might be called a program; the same tool on your phone is called an app.

Do I need to pay for apps?

No. Many apps are free, supported by ads or optional paid features. Others cost money upfront, usually a few dollars. Some use a subscription model where you pay monthly or yearly. You choose based on your budget and what the app offers.

Can I use the same app on my phone and computer?

Sometimes. If a company makes versions for both, you can use the same app on each device—though you may need separate downloads. Some apps (like web apps) work on any device through a browser. Others are built only for phones or only for computers.

What happens to my data if I delete an app?

Data saved inside the app is usually deleted when you uninstall it. However, if the app syncs data to the cloud (like Gmail or Google Drive), your data stays on the company's servers and you can access it again if you reinstall the app or use it on another device.

Why does an app need permission to access my camera or location?

Apps request permissions for features they actually need. A video chat app needs camera access. A maps app needs your location. You can usually grant or deny these permissions when you first open the app, or change them later in your device's settings. Deny any permission that doesn't make sense for what the app does.