区别主要是意思上的,语法上都作状语
1.引导时间状语从句：意思是“每当,随时”,=when
I'd like to see you whenever it's convenient.在你方便的时候我想来看看你.
Come whenever you like.你随时想来就来.
2.引导让步状语从句,= no matter when,意思是“不论什么时候,都.”
例如：I'll wait for you whenever you come.
You can eat food free in my restaurant whenever you like.
无论什么时候你都可以在我的餐馆里免费吃饭.