So "things" are countable, "stuff" is uncountable, but we still use them much the same. You just have to be careful with those quantifiers, much, many, a lot of, not enough, things like that.
所以「things」是可數的,「stuff」是不可數的,但兩者用法大致相同,只需要小心量詞的使用,像是 much (很多)、many (很多)、a lot of (很多)、not enough (不夠),之類的。