Can someone help with Korean?

Okay...so for the Korean language, I have the alphabet down, but a few questions...so the character that's 'ng', you put it at the beginning of a word if it doesn't start with a consanant, but it's silent, right? Also...I understand that you 'stack' characters...how many characters per stack? I keep writing words then going back and checking but it's all wrong...can someone help?