When saying "It's not yours" in French, you say "Ce n'est pas le tiens."
I don't understand what the "le" does or means. Why is it there and what purpose does it serve?
Merci d'avance! -Pickletoepi
Also, if the object that is "yours" is feminine it is la tienne for singular and les tiennes for plural.
Ex "The dress is yours" → La robe est la tienne.
and "The shirts are yours" → Les chemises sont les tiennes.
Remember, this is the familiar way of expressing "yours".
Formally you have le vôtre, la vôtre (single owner) and les vôtres (multiple owners of masculine or feminine gendered objects).