Something, nothing, somebody, nobody, in Spanish

algo - something

nada - nothing

alguien - somebody

nadie - nobody

Yo tengo algo. (I have something.)

Yo conozco a alguien. (I know somebody.)

In English, we cannot use double negatives:

We say either I have nothing or I don't have anything. (We use anything instead of nothing in negative sentences.)

In Spanish, we must use double negatives:

Yo no tengo nada. (Lit. I don't have nothing.)

Yo no conozco a nadie. (Lit. I don't know nobody.)

We cannot use nada or nadie in affirmative sentences.

I have nothing and I don't have anything can only be translated into yo no tengo nada.

I know nobody and I don't know anybody can only be translated into yo no conozco a nadie.