Hangeul letters with alternate pronunciations?

I was reading the vocabulary in Hangeul and came across a few words that used letters for different sounds from what they usually are. Some words used "bieup" but it was pronounced as an "m" instead of a "b". (example: "bangapseumnida" in the third syllable) Some words use "shiot" with a "t" sound (example: "shiot" second syllable) instead of an "s". There were also some that use a "tsangshiot" to make the "sh" sound instead of "ts" or "t" (example: "ssi" the honorific) Are these exceptions, rules, or am I reading them incorrectly?

Also it seems the "shiot" is pronounced as an "sh" sometimes. I was also wondering if there was a set rule for when "rieul" is pronounced as an "r" or "l".

What is known as nasal assimilation happens when a stop consonant (ㅂ ㅃ ㅍ) occurs before a nasal consonant ( ㄴ ㅁ ㅇ although ㅇ doesn't appy here as it never appers in the initial position ). when this happens, the stop consonant assimilates to the nasal sound that is produced using the same point of articulation: ㅂ ㅃ ㅍ ---> ㅁ Example: 법망 ---> [범망] 돕는다 ----> [돔는다] 앞마당 ----> [ 암마당] 없는 ----> [엄는] hope this helps.

For ㅅ and ㅆ When its in the final consonant position it is pronounced like a t or d. When ㅅ is in the Initial position it is pronounced like S. Example: 살; sal 못; mot 씨; Shi 갔; Gad

Hi Catiesam and Jeremy, Thanks for your help Jeremy! For the ㄹ it is pronounced closer to an R when followed by a vowel (or special consonant): 이름 : ee-reum 사랑 : sa-rang When a ㄹ is followed by another ㄹ or ㄴ, it is pronounced as an L. For example: 한라산 - hallasan 빨라 - bballa I hope that helps!