Am I French?
Provided that you did not loose your French citizenship (be it voluntary or involontary) at some point, you are French if you can tick at least one of those 2 boxes:
While being born in the US grants you American citizenship, to be endowed with French nationality by jus soli (Latin for "right of soil"), you need to be born in France to at least one parent who was born in France.
That said, this still remains the simplest way to be French, in regard to proof of nationality: in most cases, your full birth certificate will be proof enough.
The other way to be born French is jus sanguinis, which means "by decent": is French the child whose father and/or mother is French and already was at the time of birth.
That might sometimes be more difficult to prove, and you might need, to ascertain your French citizenship (for passport or registration of birth purposes, for instance), to produce a "certificat de nationalité française".