The expression plain base+ㄹ 수 있어요 or 없어요 which means can or cannot <verb> also corresponds to the meaning of plain verb expression whether positive or negative. Only, the pattern conveys possiblity and or ability.
The expression ㄹ 수 없어요 (-l su opseoyo) also means the same as the negative expression 못 followed by verb as in the case of 갈 수 없어요 (kal su opseoyo) is the same as 못 가요 (mot kayo); the first expression meaning cannot go and the second one emphatically means cannot go (sure that the person cannot go).
Here are some applications of this verb ending:
1. 내일 후에 시험 집에 갈 수 있어요. (Naeil hue shiheom jipe kal su isseoyo). I can go home tomorrow after the exam.
2. 오늘 아침 도서관에 올 수 있어요? (Oneul achim dosogwane ol su isseoyo?) Can you come to the library this morning?
3. 새 가방이 볼 수 있어요? ( Sae kabangi bol su isseoyo) Can i see the new bag?
4. 동생이 파티에 갈 수 없어요. (Dongsaengi pati.e kal su opseoyo) My younger brother cannot go to the party.
5. 내가 바뻐서, 이메일 답장을 보낼 수 없어요. (Naega papposo, email dapjangi bonael su opseoyo) I cannot send my email reply because I am busy.
It Started with Hangul 
안녕하세요. 우연히 이 곳을 찾았어요. ^^
I was impressed with your passion. gl2u !!
well, I found a thing that need to correct. 1st one is a little bit strange, actually, it’s wrong.
‘내일 시험 후에 집에 갈 수 있어요.’ is better.
‘내일 시험이 끝나고(면) 집에 갈 수 있어요.’ is the best.
If u have any Q about Han-gul or Korean something, mail me. I’ll help u (but, my Eng is not good lol)
lmfaokr@yahoo.com
hi jason thanks for dropping by a comment… i posted this late in the evening after office… yeah i guess i messed with the particles there =)
wah ,, i was Research about this gramar ^^””
and i understand it now ^.^
any way im learing hangul right now ^^
and sometimes i have Qs and i don’t find the answer can i take your e-mail ^^