It's kind of easy but there's more to it when you wanna start reading Korean.
When there is a "ㅇ" consonant at the end of the letter its a "ng" sound. Say I have 바 and I decide to add a "ㅇ" consonant at the end it would be 방 bang.
When you put "시" together it's pronouced "shi". Sow hen ever you see a ㅅ consonant and a ㅣ vowel together it's "shi".
When ever you see a ㅈㅅ or a ㅊ constant at the end of a letter it basically turns into a "t" sound or it sounds like your stopping your sentence. Ex: 꽃 kkot (means: flower).
I hope this make sense; I doubt it does, but I tried.