Mandarin Chinese

This is the most populous dialect of Chinese, but it won't help you much in Chinatown in NYC, cause people speak Cantonese there.

http://www.mdbg.net/

http://www.chinese-tools.com/learn/chinese

By far the most difficult aspect of Mandarin is learning the characters. In grammar, however, it is very much more accessible and simple than Japanese and Korean.

How did you learn Mandarin?