No, firstly, with 'sen' and the verb 'to be', you need to add a suffix 'sın' in this case to give the meaning 'You are a woman'. Likewise with 'siz' you need to add a suffix 'sınız, 'as Marko195 points out. Secondly, it seems that 'sen' is used for one person and 'siz' for several, just as we used to have 'thou' and 'you' in English, and the 'siz' form is also used as a polite form, like 'vous' in French.
I have a question. I do not know if I understand well but thanks to the first lessons I got that the verb «to be» is implicit in the present tense: so, if I say «O bir kuş» this will be translated like «He is a bird» or «That is a bird» (I know that to bring an example with the third person it is not the best, but it is the one that i remember). What I want to ask it is: If I write «Sen bir kadın» it does not mean «You are a woman».
Ok. It's a rule in Turkish for the syllables to be in vocal harmony. The rule is: When you need to add a suffix, naturally, it must be in one of the two groups (the two vowel groups in Turkish)
Kalın: a,ı,o,u. (Thick) İnce: e,i,ö,ü. (Fine)
The rule goes like this:
a,ı ==> ı e,i ==> i o,u ==> u ö,ü ==> ü
So, the suffix is (sin) if it was preceded by (e/i) as the last vowel in the word like in: "Sen erkeksin" = "Sen erk(e)k-sin"
But would turn into (sın) if it was preceded, as in this case, by (a/ı) as the last vowel in the word. Thus... "Sen kadınsın" = "Sen kad(ı)n-sın".
It's not just here, vocal harmony is a thing to be applied whenever you wanna add a suffix to a word (there are some few exceptions) wether it was in possession suffix, accusative suffix...