Your version of Outlook Web App has four apps installed by default. These are Bing Maps, My Templates, Suggested Meetings and Unsubscribe.
It's possible to add more apps from the the Office Store.
Click on the settings cog:
Then Options > Apps > + > Add from the Office Store.
If any apps cause problems, then we recommend you uninstall them. We may ask you do do this if you need support with Outlook Web App.