二者词性不同，自然用法也不同：however是个普通副词，whereas是连接性副词，用于引导从句。
例：
1. She has authentic charm whereas most people simply have nice manners. 她有真正的魅力，而大多数人只是有礼貌而已。
划线部分是whereas引导对照状语从句。
2. She has authentic charm. However, most people simply have nice manners. 她有真正的魅力，而大多数人只是有礼貌而已。
这是用however改写上句后的样子，however用作一个普通的副词，通常后加逗号。
