"I am not a girl."
Translation:Εγώ δεν είμαι κορίτσι.
Would greek people use ένα in this sentence? And is είναι δεν incorrect?
While including ένα is not really incorrect, it would not be used. I suggest reading spdl79's comment in this discussion https://www.duolingo.com/comment/23893917, he's figured out how this indefinite article really works!
Δεν needs to be before the verb, always. There might be something between δεν and the verb, but they have to be in that order. Same goes for μην+verb in subjunctive/imperative.
Completing this one without hints, I entered "δεν είμαι κπρίτσι", sans Εγώ, and it still counted me as correct. Now, this lesson showed up very early for me, and I still don't quite have pronoun use down yet, let alone conjugations, but it's been made clear to me that "Είμαι" is specifically the first person singular form of "Είναι", so I left the pronoun out figuring it was okay. Is the pronoun still required when using conjugated verbs? It said I was correct but I just wanted to verify.
Well done. First that you tried it without hints and that you left off "Εγώ"
The personal pronouns are always optional, in fact, Greeks don't use them except for emphasis etc. You will find them in the first skills but later they are not often used. So, of course, the sentence is correct without "εγώ".
In the Tips & notes accompanying Basic 2, there is an explanation of this and other items including a conjugation of a regular verb.
Hope that helps.