I found there are two adjectives to mean "sad" in Korean - 섭섭하다 and 슬프다. But I don't understand the difference between the two.
What is the difference and how can I use them apart properly?
'섭섭하다' is used when real situations, events or results are different from something one looks forward to. The subject of '섭섭하다' is usually people rather than situation.
For example, I expected my lovers to give me some presents for my birthday, but he didn't. So, you can say '나는 그에게 섭섭하다'.
In this case, it is possible to feel like both '섭섭하다' and '슬프다'
'섭섭하다' is similar to '서운하다'
'슬프다' is very very similar to 'sad' or 'blue'.
For example, 슬픈 결말 (sad ending) 나는 그녀와 헤어졌고, 너무 슬펐다. (I broke up with her and felt sad.)