Questions & Answers about Il mio amico che cammina nel giardino è alto.
In Italian, a possessive adjective like mio usually goes together with a definite article:
- il mio amico = my friend
- la mia casa = my house
- i miei libri = my books
So il mio amico is the normal pattern.
A common exception is with many singular family members:
- mio padre
- mia madre
- mio fratello
But amico is not a family-member noun, so the article il is normally used.
Amico is the masculine singular form, so it refers to a male friend.
- amico = male friend
- amica = female friend
Because the sentence says il mio amico, everything agrees with a masculine singular noun.
Che is a relative pronoun here. It means who, that, or which, depending on the context.
In this sentence, che cammina nel giardino describes amico:
- il mio amico = my friend
- che cammina nel giardino = who is walking in the garden
So che links the noun amico to the description that follows it.