* Les filles: This is the most common and general way to say "girls."
* Des filles: This is used when referring to girls in a more general or unspecified way, like "There were some girls there."
* Des jeunes filles: This is a more formal way of saying "girls," and often implies they are young.
* Des demoiselles: This is a very formal way of saying "girls," and is rarely used nowadays.
The best way to choose the right word depends on the situation and your desired level of formality.