请帮我讲解一下英语单词的用法.

请帮我讲解一下英语单词的用法.
1 percent percentage
2add addition addtional
3confusing confused confusion
4complain complaint
另外请帮我讲解一下表语从句的语法!
还有other states have a sales tax,which is charged to any item which you buy in that state.这个句子中为什么用to!