No credits for doing well. This game seems to be unique on Internet in that all players compete on equal basis. No buying gismo's to get an advantage.
Each game world is a separate game, so the 5cr start fee applies, plus 1cr per game week so you can drop out of a game if you want to, though that 5cr start fee does allow you 4 starts in the game if things go wrong, or you want to explore the opportunities in another continent.
The short games are not particularly good value as they are also 5cr at start up. The easy format (more capital. better fares etc) doesn't actually teach you much about competing in the long games.
To hone your skills join a long game near it's end and find a Base where there's room for another player. When the next long game starts you have a good idea where to start, even if that base is already occupied you at least know the country well enough to try a different first base in an area you know.
Remember it is for fun, the big players keep on playing so it's addictive too, but you are probably already hooked.
Trev of 11Air and Spectrum Alliance