快速答案
nada 指事物，ninguém 指人。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
nada
nothing or not anything
Use nada for the absence of a thing, action, or amount.
ninguém
nobody or not anybody
Use ninguém for the absence of a person.
如何选择
- nada: Choose nada if the sentence points to the absence of a thing, action, or amount.
- ninguém: Choose ninguém if the sentence points to the absence of a person.
例句
Não comprei nada.
I did not buy anything.
Ninguém chegou cedo.
Nobody arrived early.
常见误区
When nada or ninguém comes after the verb, Portuguese normally also puts não before the verb.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 nada，一次用 ninguém。如果两个版本都可以，说明意思怎样变化。