A noun is a person, place or thing. In French all nouns are masculine or feminine, this is called “gender” (le genre). When a noun is masculine you have to use un (a/an) or le (the) :
Un garçon (a boy) / Le garçon (the boy) 
Un coq (a rooster) / Le coq (the rooster)
When a noun is feminine you have to use une (a/an) or la (the) :
Une fille (a girl) / La fille (the girl)
Une poule (a hen) / La poule (the hen)
Here are more nouns, can you tell their gender ?
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