Maybe the app needs more time to load or it is being updated at the moment. Try opening the app after a few minutes (once the updating process is complete).
Maybe an app you recently installed prevents another app from launching. For instance, if you install a new video player, it might prevent the inbuilt video player from loading. In this case, you need to remove the new video player to make the inbuilt one work. The same solution applies to other apps, too.
Some apps requre Internet connection in order to load. Apps should load even if the device is not connected to the Internet (and notify you about that), however exclusions are always possible. Ensure that your device is connected to the Internet and once it is, open the app.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.