English has two types of articles: definite (the) and indefinite (a, an.) The use of these articles depends mainly on whether you are referring to any member of a group, or to a specific member of a group:
Indefinite (a or an) Definite (the) Singular a dog (any dog)
an apple (any apple)the dog (that specific dog)
the apple (that specific apple)Plural some dogs (any dogs)
some apples (any apples)the dogs (those specific dogs)
the apples (those specific apples)