Learn Italian: Mio fratello è arrivato undicesimo nel campionato. - My brother finished eleventh in the championship.

To form ordinal numbers from 11 upwards, you drop the final vowel of the base number and add the suffix -esimo. So, undici becomes undicesimo. Because ordinal numbers act like adjectives, it ends in -o to match the masculine singular subject, Mio fratello.

The translation says my brother finished, but doesn't è arrivato mean arrived?

Yes, it literally means he arrived. In Italian sports and competitions, the verb arrivare is commonly used to express what place someone came in. You are literally saying he arrived eleventh.

Why is there no article before Mio fratello? Shouldn't it be Il mio fratello?

You do not use a definite article like il or la with possessives when referring to a singular, close family member. So it is just Mio fratello. If it were plural, you would need the article and say I miei fratelli.

Why do we use è instead of ha for the past tense of this verb?

The verb arrivare describes motion. In the past tense, most verbs that indicate movement from one place to another use essere as their helper verb instead of avere.