une chanteuse camerounaise

C'est une chanteuse camerounaise. Elle étudie à Paris et elle chante en anglais.// She is a Cameroonian singer. She studies in Paris and she sings in English.

 

Today we were doing the professions. It took our teacher a goodish while to explain the difference between C'est une(un)... and Elle/il est ...  and why the indefinite article is used in the first construction and not in the other.

Interestingly (unless I am mistaken), it would be easier for him if everybody knew Russian. First construction is a direct analog of  "Это одна (или некая) певица" and the second "Она певица".