From the publisher's website:

In Balloon Cup, the players compete in several short balloon flights (hops) to collect the colored cubes associated with each hop. When a player has collected enough cubes of a given color, he earns the trophy card for that color. Players may even trade 3 otherwise useless cubes for 1 they can use. The first player to earn 3 trophy cards is the winner! Each player has a hand of eight balloon cards. The players play their balloons on mountain or plain hops. Players play their high-valued balloons on the mountains and their low-valued balloons on the plains. Players usually play their balloons on their side of the hops, but winds (and cunning) can cause them to play on their opponent’s side, a move that can ruin their opponent’s plans. Errata: Although very unlikely, it is possible that players could experience a situation in the game where it is impossible to complete one or more of the available hops due to the distribution of cubes on them. To prevent this, players may want to restrict the number of cubes on all tiles as shown below: there should be no more than 2 grey cubes, there should be no more than 3 blue cubes, there should be no more than 4 green cubes, there should be no more than 5 yellow cubes, and there should be no more than 6 red cubes.