Your phone might have temporarily lost its Internet connection, or you might be trying to download an app that's too big to download over your phone's cellular data connection. If you're trying to download an app larger than 20 megabytes (MB)—this applies to many games—you'll need to connect to a Wi-Fi network, or connect the phone to your PC and use the Zune software.
Make sure you have a connection. On Start, tap Marketplace.
At the bottom of the screen, you'll see the number of incomplete downloads. Tap it to see the downloads queue.
Tap and hold the stuck app or game, and then tap Retry. If it doesn't work, connect to Wi-Fi and try again. You can also connect your phone to your computer, start the Zune software, and download the app via Marketplace on your PC.
One common cause of a lost Wi-Fi connection is a screen time-out, which pauses your connection and can prevent apps from downloading. If you're downloading lots of games and other large apps on your phone via Wi-Fi, you might want to temporarily increase the screen time-out period or disable it. To learn how, see Lock screen FAQ.
The people who create apps and games for Windows Phone are constantly making tweaks and improvements, fixing bugs or adding new features. When a newer version of an app you own is available for download in Marketplace, you'll know it.
On Start, you'll see a number on the Marketplace Tile that indicates how many of your apps have updates available.
When you open the Marketplace Hub, you'll also see a message at the bottom indicating you have updates available. Tap the message to see the list and start installing them.
When you buy apps or games from Marketplace on windowsphone.com, there are three ways to have them delivered and installed on your phone. None require that you plug your phone into your computer. Here are the options, from fastest to slowest:
Many apps or games you buy from Marketplace are designed to take advantage of specific hardware and software features of your Windows Phone. For example, a photo app might need to use your phone's camera, and a restaraunt guide might need to know your location to provide nearby recommendations.
You can see what features an app requires by looking at the app's details screen in Marketplace. Apps are required to ask you for permission before using certain phone features. Here's a list of features you'll see listed:
App Connect is a feature of Windows Phone 7.5 that makes apps more useful and convenient—and that can also help you discover apps you didn't know you needed. You'll see evidence of App Connect in several areas of your phone. The Pictures Hub, for example, shows photo apps you've downloaded; the Music + Videos Hub lists apps related to music or video. Launching an app from either of these places can sometimes have added benefits: Depending on the app, Windows Phone might be able to send relevant information to the app to save you time—for example, the name of the artist or song you're playing. (In many cases, it's up to the app developer to make behavior like this possible, which is why you won't find all your photo-related apps in your Pictures Hub, for example.)
App Connect also comes into play when you do web searches, especially for movies, products, and places. In some cases, you'll see a relevant app suggestion right at the top of your search results. In other cases, you'll see apps mentioned when you drill into the details of a search for movies, products, and places—like a cinema app when you're looking at showtimes.