what/whatever;that/what; who/whoever

1）what = the thing which；whatever = anything
　　　What you want has been sent here.
　　　Whatever you want makes no difference to me.
2) who= the person that　 whoever= anyone who
　　 （错）Who breaks the law will be punished.http://yingyu.chazidian.com
　　 （错）Whoever robbed the bank is not clear.
　　 （对）Whoever breaks the law will be punished.
　　 （对）Who robbed the bank is not clear.
3) that 和 what　
　　当that引导定语从句时 ，通常用作关系代词，而引导名词性从句时，是个不充当任何成分的连接词。宾语从句和表语从句中的that常可省略。What只能引导名词性从　句， 用作连接代词，作从句的具体成分，且不能省略。
　　I think (that) you will like the stamps.
　　What we need is more practice.