~(으)ㄹ 수 있다/없다 is used to indicate an ability or possibility of doing something. This form is constructed from the noun-modifying ending ~(으)ㄹ, the noun 수 “means/way,” and the verb 있다 “have/exist.” For negation, 없다 “not have/not exist” is used instead of 있다. ~(으)ㄹ 수 있다 is equivalent to English translation “one can do/be” or “it is possible to,” as shown in the examples below:

피아노를 칠 수 있어요.

“(I) can play a piano” or “(It) is possible to play a piano.”

서울에 갈 수 있어요.

“(I) can go to Seoul” or “(It) is possible to go to Seoul.”

그 책을 읽을 수 있어요.

“(I) can read that book” or “(It) is possible to read that book.”

On the other hand, ~(으)ㄹ 수 없다 is used to express “cannot do/be” or “it is not possible to.”