The definite article in Italian

Masculine

Il : for masculine singular nouns which start with a consonant.
Il giorno ( The day)
Il  cavallo ( The horse)

L’ : for masculine singular nouns which start with a vowel.

 L`albero ( The tree)

Lo : for masculine singular nouns which start with:

Lo is used for masculine singular nouns beginning with a Z or S+consonant.
ex..
Lo studente ( The student )
 Lo zio ( The uncle)

I : for masculine plural nouns which start with a consonant.
I cavalli (The horses)
I ragazzi (The boys)

Gli : for masculine plural nouns which start with a vowel, s + consonant, z, y, ps, pn, x or gn.

Gli angeli ( The angels )
Gli orologi (The watches)

Feminine

La : for feminine singular nouns which start with a consonant.
La casa ( The house)
La sedia (The chair )

L’ : for feminine singular singular nouns which start with a vowel.
L`ape ( The bee )
L` idea ( The idea )

Le : for feminine plural nouns which start with a vowel or a consonant.
Le penne ( The pens)
Le sedie ( The chairs )
Le case ( The houses )