cannot comprehend this from my text book. How to understand this?

Consider the order types w and n. It is easy to see that n+w=w. In fact, if finitely many terms are written to the left of the sequence 1,2,...,k,..., we again get a set of the same type(why?). On the other hand, the order type w + n, i.e., the order type of the set {1,2,...,k,...,a1,a2,...,an} is obviously(?) not equal to w.