i won't go into details in my answer since it urges lengthy explanation and i also consider myself incompetent of doing so.
mostly, spoken korean is the same with the written one. you can also simply adapt and create a new assimilated korean word by writing the word as it's pronounced. however, as you start reading and referring to the references, you will find exceptions, a hefty amount of them.
i will show you some of these exceptions. first we'll define two terms: written language (쓰는 말) and pronounciation (발음).
1. ㅂ at the end of a syllable should be pronounced as ㅁ if the next syllable starts with ㅁ or ㄴ
eg:
a) 쓰는 말: 감사합니다 (kam-sa-hap-ni-da)
발음: 감사함니다 (kam-sa-ham-ni-da)
b) 쓰는 말: 없는 (eop-neun)
발음: 엄는 (eom-neun)
2. ㄷ and combinations thereof (ㅌ,ㅆ,ㅅ) at the end of a syllable should be pronounced as ㄴ if the next syllable starts with ㄴ
eg:
a) 쓰는 말: 있는 (id-neun)
발음: 인는 (in-neun)
b) 쓰는 말: 얻는 (eod-neun)
발음: 언는 (eon-neun)
3. ㄱ at the end of a syllable should be pronounced as ㅇ if the next syllable starts with ㅁ or ㄴ
eg:
a) 쓰는 말: 박물관 (pak-mul-gwan)
발음: 방물관 (pang-mul-gwan)
b) 쓰는 말: 먹는 (meok-neun)
발음: 멍는 (meong-neun)
4. ㅌ at the end of a syllable should be pronounced as ㅊ if the next syllable starts with 이
eg:
a) 쓰는 말: 같이 (kat-i)
발음: 가치 (ka-chi)
5. there are also some basic rules for pronounciation, for eg. if a syllable ends with consonant and next syllable starts with vowel, you have to move the consonant to the first character of the next syllable as you pronounce it, unless another exception applies (see 4)
eg:
a) 쓰는 말: 알아요 (al-a-yo)
발음: 아라요 (a-ra-yo)
b) 쓰는 말: 언어 (eon-eo)
발음: 어너 (eo-neo)
6. etc (others may add)