设计n层应用程序时出现的混乱

I have been having a difficult time understanding how to separate my program into a n-tier application with 3 layers (BLL,DAL,UI). I have so much confusion on the subject that I don't know where to begin. I have looked at videos, articles, and application examples, but I find it hard to comprehend. There seems to be a lack of consistency from one example to the next. Is there any resource I can look at that is extremely thorough on the subject?I have been having a difficult time understandi