Learn Italian: Il nonno dorme da solo per la salute. - The grandfather sleeps alone for his health.

While solo can mean 'alone', it often means 'only' or 'just'. Adding da creates the phrase da solo, which specifically means 'by oneself' or 'alone'. If it were the grandmother sleeping alone, the phrase would change to match her feminine gender: da sola.

Why does the Italian sentence say la salute (the health) instead of 'his health'?

Italians often use the definite article (like la or il) instead of possessive words like 'his' or 'my' when the owner is obvious from the context. This is the standard rule when talking about health, body parts, and clothing.

How does the verb dormire (to sleep) work here?

Dormire is a regular verb ending in -ire. Because the grandfather (he) is doing the action, we drop the -ire and add the regular third-person singular ending -e, making it dorme.

This lesson teaches the verb stare. Could we use stare here to talk about his health?

Not with the noun salute (health), but you could rephrase the action! For example, Il nonno dorme da solo per stare bene translates to 'The grandfather sleeps alone to be well'.