The app itself works just as you'd expect. You can browse movies and start streaming right away. Any movie that's available through the desktop apps is available here. It's a little slow, but it works well once it starts streaming. The app's free, but you'll need to add the Popcorn Time repo to Cydia before you can find it:
The app's not available in the App Store, but if you have an old iOS device sitting around that you're not using, now might be the time to jailbreak.