This letter ㅅ (siot) is the tenth jamo in the South Korean (and the 7th in North Korean) writing system. Incidentally, the alphabets consist of the same letters but the differences occur because of where the stressed consonants are places in the order. But logically just like the order of the English alphabet, the letters are in arbitrary order. I digress.
ㅅ (siot) is pronounced in a variety of ways. The most simple way to remember it is that it looks like a seashell. However, it can be pronounced like an s, an sh and sometimes like a t. I get that this can be a challenge to a beginning learner. Sometimes in Korean, depending on where a letter falls in the syllable or word, and what comes after it, the pronunciation is different. When ㅅis followed by some vowels, it becomes a sh sound. Since we haven’t gotten to the vowels in this series yet, I won’t go into detail as this is intended to be a basic introduction. But a quick google search will provide you with a multitude of reading materials on the nuances of the Korean language.
The double consonant ㅆ (sang siot) is a stressed s sound. But this consonant often comes at the end of a syllable and in that case it is pronounced with a t sound like ㄷ(t).
Don’t Get Overwhelmed
I want to end by reminding you that ALL languages take a lot of time to learn and learning Korean is going to be hard learn. My students often ask me “what language is the easiest to learn?” and my honest answer is that there is not one single language out there that is easy to learn. Korean is a challenging language to learn for English speakers. I am still a novice learner myself, I’ve only been learning (at my own pace and only self directed) for just at a year. I started June 2019, and I am still so achingly beginner it makes me frustrated sometimes. But patience.