说明：  NS2入门指导　，因为我当时比较盲目看了很多兑现在一点儿用都没有的资料。为了能让写的东西真的对新手有所帮助，刚所以总结了一下，希望能起到抛砖引玉的作用。
(NS2 elementary guidance, as I have read many more blind honored in a little bit with no information. In order to allow write things really help to newcomers, just sum it, and hope to play the role of feedback.)