if you want to learn something or in the future you want to learn, it will be (naraitai、習いたい）. but,you are going to learn somrthing or learn now,it mean (narau ) mabe depends on sutiation.

it's 'naraitai'. plain(ru-verb) of 'learn' is 'nara-u（習う）'. if you want to express your willingness, transform ru-verb 'nara-u（習う）' into i-adjective 'nara-i（習い）', then, add a willingness expression part "tai（たい）". so, nara-i-tai（習 - い - たい） is the correct conjugation! reference http://www.guidetojapanese.org/desire.html#part2