Learn Italian: Il giornalista esagera, non ci credo. - The journalist is exaggerating, I do not believe it.

The pronoun ne replaces phrases starting with di. However, the verb credere takes the preposition a when you mean "to believe a fact or statement" (credere a qualcosa). To replace a phrase starting with a (meaning "to it" or "in it"), we use the clitic ci, not ne.

Why does giornalista take the masculine article il if it ends in "-a"?

Nouns for professions ending in -ista (like giornalista, dentista, barista) are unique: they end in -a for both masculine and feminine in the singular. We use il here because the sentence refers to a male journalist. If it were a female journalist, it would be la giornalista.

I sometimes confuse ci and lo. Could I say non lo credo here instead?

In Italian, to express "I don't believe it" (referring to a situation, story, or exaggeration), you use credere a, which gets replaced by the indirect pronoun ci. If you use lo, it changes the meaning slightly to "I don't believe him" or "I don't believe so." Non ci credo is the standard, natural way to say "I don't believe it."