Hello Hong, A very good start would be the website: livemocha. It is just like italki, but have some extra usefull things. You will find there a special program to teach you chinese - german. There are also 4 levels from beginner to advanced. You can find there partners who do the same study like you, and also will have a privat teacher to help you. That is a professional teacher payed by livemocha. And best of all maybe, its totaly free, so you only have to study. I hope this will help you. Bye bye