Oh yes: you have to collect acorns in flight, but while avoiding trees, owls and bad acorns. Depending on how far you can get on a flight and how many have acorns you here collected, is obtained as the currency - so what good? - Acorns, exactly.
With these, you can then upgrade their croissants - but these upgrades usually have only unique feature -> bad. (Called goals) The achievement of various objectives brings additional points in the form of acorns.
So you need to upgrade a lot of acorns, you can buy these for real money in the App Store -> very bad, real rip-off!
Comparable hereby perhaps the game "Hill Climb Racing", which clearly but suits me more, and that is also appreciated by my little granddaughter, who now (25/04/2015) but also like this game.