Italian makes plurals by changing the final vowel, not by adding -s. A word ending in -o becomes -i, one ending in -a becomes -e, and one ending in -e becomes -i. The article changes with it: il becomes i, la becomes le.
Examples
- Ho due fratelli e tre sorelle.
- I have two brothers and three sisters.
- Gli alberghi sono pieni.
- The hotels are full.
- Vorrei due caffè, per favore.
- I'd like two coffees, please.
The mistake to avoid
Adding an -s is the commonest beginner error - there is no -s plural in Italian at all.
Where this fits in
Numbers, days, time, Italian A1: Count, talk about days and months, give the time, and handle numbers in real situations.