-(으)ㄹ 수 있다 is a Korean grammar topic you use to express you can do something or something is possible. -(으)ㄹ 수 없다 is its negative. Both are easy to use.
To express you know how to do something in Korean, you can use the Korean grammar pattern -(으)ㄹ 줄 알다. To express the opposite, you use -(으)ㄹ 줄 모르다.
Expressing an impossibility for something to happen or your inability to do something, can be done with using the negation -지 못하다 or simply 못 in Korean.