Learn Italian: Lui è l'uomo.

You learned that il is the article used for masculine nouns. However, because uomo starts with a vowel, Italians drop the vowel of the article and add an apostrophe to make it flow better. So, it becomes l'.

Can I just say È l'uomo without the lui?

Yes! Italian is a "pro-drop" language, meaning it often drops the subject pronoun. Because the verb è already tells us the subject is "he", "she", or "it", you can simply say È l'uomo. Including lui adds emphasis, as if you are pointing out that HE is the man.

Why does the verb è have an accent mark on it?

The accent mark is very important because it changes the word's meaning. With the accent, è means "is". Without the accent, e means "and".

Does uomo follow the regular gender rules?

Yes. In Italian, most singular nouns ending in -o are masculine, and uomo (man) fits this rule perfectly.