Learn Hardcore Italian: Trovo un codice nel libro rosso.

Trovo is the first-person singular present indicative of trovare (“to find”). In English you say “I find,” so in Italian you use trovo (“I find”). If you wanted the infinitive, you’d keep trovare (“to find”), but the sentence would need a different structure (“Voglio trovare un codice…” etc.).

Why is there an indefinite article un before codice? Could I use il or omit the article?

Un is the indefinite article meaning “a” or “an,” indicating you’re talking about any code, not a specific one.

If you know exactly which code you’re referring to, use the definite article: il codice (“the code”).
In Italian you generally can’t omit the article with singular countable nouns, so you wouldn’t say just codice here.

What does nel stand for? It isn’t just in, right?

Nel is a contraction of in + il.

In is the preposition “in.”
Il is the masculine singular definite article.
Put together, in + il libro becomes nel libro (“in the book”).

Why is the adjective rosso placed after the noun , unlike English where adjectives come first?