As you would expect from this sort of app, it will allow you to stream a movie or TV show that you have purchased or rented over Wi-Fi. And, as you would expect because of Apple's app restrictions, you can't actually buy or rent any content through the app itself. For that, you'll have to use either Safari or Chrome on your Apple device, or any browser on any computer.
The app does have some restrictions though. You can apparently only stream over Wi-Fi, not mobile data; and, there is no way to save videos for offline viewing. Also, the app is only available for users in the United States, Japan, and United Kingdom.
If you are a Google Play Movies & TV user with an iOS device in one of those three countries, this is the app for you. It's available for free in the App Store.
Download: Google Play Movies & TV