As you know, a noun is a person, place or thing. When you want to refer to a specific person, place or thing, in English you use the defnite article the, in French, because we have gender (masculine/feminine) and number (singular/plural) there are four different definite articles : le, la, l’, les .
1) “Le”
Before a masculine singular noun the definite article is le :
Le chien (the dog)
Le chat (the cat)
Le garçon (the boy)
Le train (the train)
2) “La”
Before a feminine singular noun the definite article is la :
La maison (the house)
La voiture (the car)
La chemise (the shirt)
La fille (the girl)
3) “L”
Before a vowel (the vowels are a,e,i,o,u,y) le or la become l’ :
L’ami (the friend)
L’avion (the plane)
L’enfant (the child)
L’orange (the orange)
4) “Les”
Before a masculine or feminine plural noun the definite article is les :
Les amis (the friends)
Les avions (the planes)
Les garçons (the boys)
Les filles (the girls)