Translation:A man walks.
Pro tip to remember 걷습니다: It sounds similar to "god-seub-ni-da", so I just imagine a guy WALKING on water -because....um...Gods can walk on water? The connection isn't that strong and maybe it doesn't make much sense, but thanks to this trick I learned "걷습니다" in the first lesson of verbs 1.
My cat walks, https://www.google.com/search?rlz=1C1AFAA_enUS452US526&ei=B9v3WueGE4Oq8AOTvZOgCw&q=progressive+verb+tense+in+Korean&oq=progressive+verb+tense+in+Korean&gs_l=psy-ab.12..33i22i29i30k1l2.9046.15333.0.17818.104.22.168.0.0.0.89.822.214.171.124....0...1c.1.64.psy-ab..0.11.865...0j0i67k1j0i22i30k1.0.MtQq90JChj0
Some info on the differences:
Think of 가 and 이 as being used to bring in new information, and 은/는 being used to connect what's already known to the new information.
In this sentence: 남자는 메시지가 있습니다 (The man has a message), you probably would've already known about the man with past context.
Maybe you're sitting in your office and your secretary comes in. "There's a man outside wanting to see you." They say. There would've likely been a 가 attached to the man, since it's new information that he exists.
"What does he want?" You reply.
"He (the man) has a message./남자는 메시지가 있습니다." The secretary replies. You already know about the man. He's not new information. What's new information is the message. So, 'message' is the item that will have 가 attached to it, putting more emphasis on it than the man. The man will just have 는 attached to it to attach it to the next word.
I learned this concept from Japanese, and from what I've seen so far, it seems to be the same in Korean. I never understood it when people just said "as for (item), etc. etc." when explaining は, which in Korean is 은/는, and it seems that sentence is popping up here too. I didn't even know what that meant! As for the man? How does "as for..." tell me when to use は or が (은/는 or 가/이)?
I feel like a better way to explain it would be "as for (object), which you already know about +은/는, this is what's new that exists +가/이."
So, to connect that back to the original sentence 남자는 메시지가 있습니다, it'd be like this:
"As for the man (which you already knew about, so you'd use 는 with him), he has a message (using 가 since this is new information, so it gets more emphasis)."
Of course, if you're introducing the man and the message in the same sentence, you'll just put 가/이 on whatever needs more emphasis or could be considered more important.
남자는 메시지가 있습니다. There is a man and he has a message, but the part with more attention/emphasis is the message he has.
남자가 메시지는 있습니다. (I switched 가 and 는). There is a man and he has a message, but what's getting more attention is that there's a man that has the message. 》Maybe the secretary from before came in and said "There's a message for you," making the message already known. "Who has it?" You ask. "A man has the message," replied the secretary, placing the 가 on the man because he's the new information.
Hopefully this makes more sense to anyone reading it! I know I could've used a better explanation when I first learned how this stuff worked, heheh.
은 / 는 is the topic marker and it is more general. 이 / 가 is the subject marker and it is more spesific.
Exp: 남자는 갇습니다 - A man walks. 남자가 갇습니다 - The man walks.
I explain this from what I understood and based on others' comment. Idk if this is correct or not. So maybe someone could explain it better than me. Sorry if i'm wrong.
I thought that we should recognize the subject in the sentence and attache 가 to it... but this sentence is confusing me totaly now because even if the man is the subject they attached 는 to it, please if someone have a great explanation for both of those two tricks may explain to us