Nouns are pluralized by changing the final vowel. Masculine nouns change their ending to -i (un fratello → due fratelli, un giornale → due giornali). Feminine nouns change their ending from -a to -e (una sorella → due sorelle) or from -e to -i (una chiave → due chiavi).
The definite article (the) is different for plural nouns, and different for the two genders (i fratelli, le sorelle). There is also a special version for masculine nouns that start with a vowel (gli uccelli).
The word for never in Italian is mai. This word is usually used in a double negative structure (Non vado mai a Roma, I never go to Rome), just like the word niente, nothing.
The word for one in Italian is exactly the same as the indefinite article. There is no difference between saying a cat and one cat - they are both un gatto. Likewise, una casa can mean either a house or one house. The only way to tell the difference is from context and intonation.
