Does Korea have third person pronouns for he/she? I read them in the dictionary, but someone mentioned they aren't really used. He/she pronouns are mostly used in books, but not conversations. Is this correct?
Yes, there are 그 for "he" and 그녀 for "she" (and 그들 for "they"), but uses of these pronouns are rather peculiar. They are used mostly in writing (especially novels) and occasionally in formal speeches. They are rarely used in everyday speech.
How rare? They are very very rare in normal speech. I personally have never used or heard any of them used by a family member or friend in my entire life, and this could also be true for the majority of Korean people.
In conversation, we use 그 사람 (genderless), 그 남자 (he), 그 여자 (she), and 그 사람들 (they) most commonly. There are also 그애, 그 남자애, 그 여자애, 그애들 for children and sometimes young adults, and 그분, 그 남자분, 그 여자분, 그분들 when referring to adults more politely. All these words are compound expressions (e.g. 그 = that, 사람 = person) but they are effectively equivalent to pronouns. Also note that in Korean, personal pronouns are used much less than in most other languages, so there is less need for these words.
그 and 그녀 and 그들 (they) were coined by necessity when Korea started interacting with the outside world about 100 to 150 years ago, in part to translate Western literary works which used pronouns so heavily. They have firmly taken root in novels and other similar contexts such as certain formal writings or voice narration in movies and dramas, but not in ordinary speech.