Apps are the programs that are executed on mobile devices. Mobile devices come with a number of different apps preinstalled to provide basic functionality. There are apps to make phone calls, send and receive email, listen to music, take pictures, and play video or video games. Many other types of apps enable information retrieval, device customization, and productivity.

Apps are used on mobile devices the same way that programs are used on PCs. Instead of being installed from an optical disk, apps are downloaded from a content source. Some apps can be downloaded for free, and others must be purchased. Often, free apps are loaded with advertisements to help pay for development costs. Several content sources are available for Android mobile devices:

There are many other websites where Android apps can be found. These sites usually offer safe content, but sometimes they offer unsafe content. It is important to install apps only from trusted sources. If a questionable site contains a desirable app, check Google Play or the Amazon App Store to see if it can be downloaded from there instead. This will ensure that it is a safe download. The Google Play app only allows installation of apps on devices that are compatible with them.

Sometimes a website contains a Quick Response (QR) code, as shown in Figure 2. QR codes are similar to a bar code, but can contain much more information. To use a QR code, a special app accesses the camera on a mobile device to scan the code. The code contains a web link that allows the direct download of an app. Be careful when using QR codes, and only allow downloads and installations from trusted sources.

The Apple App Store, as shown in Figure 3, is the only content source that iOS users are allowed to use to get apps and content. This ensures that Apple has cleared the content to be free of harmful code, meet strict performance guidelines, and does not infringe on copyrights.

Other types of content are also available for download. Like apps, some content is free, while other content must be purchased. Content that you currently own can also be loaded onto mobile devices through a data cable connection or over Wi-Fi. Some types of content that are available include:

Push versus Pull

There are two main methods for installing content on mobile devices: push and pull. Both Google Play and the Apple App Store support push and pull. When a user runs the Google Play app or the Apple App Store app from a mobile device, apps and content that are downloaded are pulled from a server to the device.

With Android devices, a user can browse Google Play using any desktop or laptop computer and purchase content. The content is pushed to the Android device from the server. iOS users are able to purchase content from iTunes on a desktop or laptop computer that is then pushed to an iOS device.

When an Android app is being installed, a list of all the required permissions is displayed, as shown in Figure 4. A game may need to access the Internet, manage sound settings, or enable vibration, for example. The game does not, however, need to access the list of contacts stored in a smartphone. You must agree to grant the listed permissions to the app so that it can be installed. Always read the list of permissions carefully and do not install apps that request permission to access items and features that it should not need.

Sideloading

There is another way to install apps on mobile devices. Apps can be downloaded from different sources on the Internet and transferred to a mobile device through Wi-Fi, Bluetooth, data cable, or other methods. This is called sideloading. After the app is transferred to the mobile device, it can be installed by touching it using a file explorer app. However, sideloading apps is not recommended, because many sources for apps cannot be trusted. Only install apps from trusted sources and developers.