To state that you can do something or have the potential to so something, use the ~(으) ㄹ 수 있다 construction :

집을 지을 수 있어요 = I can build a house

(집 = house. 을 = object marking particle. 지을 수 있어요 = can build) (짓다 = to build)

Compare the above sentence with this sentence :

집을 지을 줄 알아요 = I know how to build a house

(집 = house. 을 = object marking particle. 지을 줄 알아요 = know how to build)

With the second sentence, it’s not the potential to do something that is being expressed, but whether one has the knowledge to do something that is being expressed. This construction will be ~(으)ㄹ 줄 알다.

To express that you can’t do something, use the construction ~(으)ㄹ 수 없다 :

자전거를 탈 수 없어요 = I can’t ride a bike

(자전거 = bicycle. 를 = object marking particle. 탈 수 없어요 = can’t ride) (타다 = to ride)

Compare it with this sentence :

자전거를 탈 줄 몰라요 = I don’t know how to ride a bike.

(자전거 = bicycle. 를 = object marking particle. 탈 줄 몰라요 = don’t know how to ride)

So to express not knowing how to do something, use the construction ~(으)ㄹ 줄 모르다