Learn French: Elle est une fille.

Le and la mean "the" (definite articles). Because this sentence means "She is a girl" and not "the girl", we need the indefinite article une. If you wanted to say "She is the girl," it would be Elle est la fille.

Why do we use une instead of un?

All nouns in French have a gender, and the words around them must match. Since fille is a feminine noun, we use the feminine word for "a", which is une. If we were saying "He is a boy," we would use the masculine version: Il est un garçon.

How do you pronounce the double L in fille?

In French, the letters ill together usually make a "y" sound, similar to the "y" in the English word "yes". So, fille is pronounced roughly like "fee-y", not "fill".

I've seen est before, but what verb is it from?

Est is a form of the verb être, which means "to be". Here, elle est means "she is". You also use this exact same word for "he is" (il est) and "it is" (c'est).