"Yes, I am a girl."
Translation:Oui, je suis une fille.
that's what I wrote...why is this incorrect..it agrees with your answer.
"Une" refers to feminine pronouns, whereas "un" is referring to masculine pronouns (ex. Je suis une fille / I am a girl) Une, or a, is feminine so it would be used here instead of un.
Mainly you can memorize it but otherwise as much as I noticed it... Male comes with un and female with une.
How do you know when to say "Oui" or "si" obviously, "si" most often means "if" but when can it mean the same as "oui"?
It means the same as in both would translate to "yes" in English, but to a French speaker they are not interchangeable.
Broadly, "si" comes after a "no" or negative
- Tu as faim? (Are you hungry?)
Tu n'as pas faim? (Aren't you hungry?)
After "yes" or "no" at the beginning of a sentence, you always put a comma. It's a rule. https://www.superteacherworksheets.com/punctuation/yes-no-comma.pdf