Aqua can do two things when it sees a Calendar (ical) attachment... ok, three:
1 - provide a preview of the invite, this is in the attachments pane when viewing a message
2 - when you tap the invite, it shows its details and lets you send a response (accepted / declined / tentative)
3 - optionally, it can save the event in the Android system Calendar
An invite/event saved in the system Calendar is then visible in the system Calendar app, and to all other (third party) apps that work with these events.
Android 4.0 is required for saving events, 4.2 is recommended.