Watch an overview of the new app on this one minute video:
This app has a number of features that may make it preferable to you over the built in email app in iOS. You will get your Outlook calendar built in to the same app. You can also attach files from DropBox, Google Drive, or OneDrive when sending attachments. The Inbox contains a “Focused Inbox” feature that “intelligently presorts your email so you can focus on what matters.” In other words, it puts less personal mail in an “Other” section so you can see personal items more quickly.
This Outlook app can also be used to manage your Gmail or Yahoo email as well. You can add multiple accounts to one device.
This link (if opened on your iPad or iPhone) will take you to the install page in the Apple App Store: