When is déanaim used? I would have expected "níl ithim," but I was thrown off by the translation for "I do" and ended up adding déanaim to the beginning - is that generally omitted in sentences where one would say "I do not ___?"
Yes — English “do-support” for negative sentences should not be translated literally.
ní is the negative particle and lenites. níl is a contraction of ní fhuil (recognize the fuil from an bhfuil) and is only used as the negative of the non-habitual present of bí (tá, an bhfuil, níl)
This means absolutely nothing to me as i have never figured out what bhfuil is. I wish someone would explain simply when to use ni and when to use nil.