I’m working through the TalkToMeInKorean Iyagi series. I notice that sometimes the verbs can be conjugated with ‘다’ and I always had thought this to be only for writing.
Sorry for the long example but this is the most recent one I have come across and it’s beginning to bug me that I don’t understand why:
그리고 그 이야기의 상당히 많은 부분은 이 나라를 바꾸겠다.
In this case I read “바꾸겠다” as being the future tense of ‘to change’ with a plain conjugation. I would have expected an 어 or 어요 instead.
While -다 ending is extensively used in writing, it is not strictly for writing only.
People use it in conversation too. -어 and -어요 will dominate, but -다 is also mixed in occasionally.
There are also some special contexts where -다 is preferred even in a conversation, like when one makes a sudden exclamation.
For example, if I was searching or trying to recall something and finally came upon it, I would most likely shout 찾았다 (I found it!) or 생각났다 (I remember now!). -다 ending in this case has a stronger and forceful nuance and separates the phrase fomr the rest of the conversation which is in -어(요) style. So it has a place in daily conversation too.
As for your example line, I think the confusion is in because of the confusing way the sentence was written. The full sentence I found is as follows:
선현우 : 네. 그리고 그 이야기의 상당히 많은 부분은 이 나라를 바꾸겠다. (아…) 더 살기 좋은 곳으로 만들겠다. (음…) 이 세상을 바꾸고 싶다.
(와, 멋집니다) 이런 이야기들 하잖아요. (네, 그렇죠) 남자들은.
This is a terribly confusing sentence even crossing the paragraph boundary.
The parenthesized parts are the listener backchanneling, so should be taken out.
It can be rewritten like so:
선현우: 네. 그리고 그 이야기의 상당히 많은 부분은 “이 나라를 바꾸겠다. 더 살기 좋은 곳으로 만들겠다. 이 세상을 바꾸고 싶다”, 이런 이야기들 하잖아요. 남자들은.
As you see, the -다 endings are all part of the quotation which is the conversation Sun had with his friend when he was in school. The transcription is done just as it is heard leaving every structuring to the reader to figure out.
Anyway, this is another example where one might use -다 in an informal conversation - a quotation. By using the more formal -다 endings, the quoted part is nicely demarcated from the rest of the conversation to aid comprehension.
It can be translated as:
Sun Hyun Woo: Yes, And a great part of those conversations went like “I will change this country. Make it a better place to live. I’d love to change the world”, stuff we always talk about. I mean us guys.
As a side, I have noticed that the TTMIK site has this tendency I consider unfortunate. In the name of a “natural dialog”, the audio materials they upload include so much meaningless interjections, greetings and all kinds of useless stuff there doesn’t seem to be that much useful content left once you strip away the fluff. They might be good for advanced learners, but for anyone at low to mid level, it seems very wasteful. In an early stage of learning, I think we need to concentrate on well constructed and substantive sentences, not the confusing styles that most native speakers indulge in.
I hope I explained it well enough.
Thank you very much for that lengthy and descriptive reply!
I had misunderstood that particular quote from the TTMIK Iyagi. I did not realize Sun Hyunwoo was ‘quoting’ how the previous conversations had gone.
The TTMIK content is certainly a fair bit above beginner. Unfortunately there is a lack of beginner content once one has gone through the Sogang 2A, Who is She, and Eating out style materials. I have had a look at the majority of the content around my level and some of it I have worked through many many times now (with a lot of listening).
The TTMIK content is diverse and the people involved all sound enthusiastic which makes it substantially easier to listen to than pretty much all the other audio material I have.
I realize that ideally I would be working my way through properly constructed and graded material - where I can be introduced to grammar and vocab at a steady pace. However there really doesn’t seem to be much. Perhaps the best place to have this kind of thing really is to work through a language textbook, doing exercises, listening to their accompanying audio CD’s.
However that moves into the realm of it turning into study where I need to set aside time to do it.
Then again content can surprise. I recently pulled an article off a new site about the discovery/proof of gravitational waves. I needed to look up a lot of the nouns but otherwise I actually understood the article pretty well I think. Pity it does not come with someone reading the audio 
Yes, I agree TTMIK provides good contents which are very diverse and with clear and natural sounding dialogues. They seem to have established themselves as one of the best Korean sites that everybody Korean learner knows.
Well organized Korean sites like TTMIK seem to be rare compared with other languages, however, which is unfortunate. Although I haven’t really searched much, I notice it from time to time from discussions going on at forums or when someone brings it up and I try to find one. Hopefully things will improve.
One interesting site I recently found was the Jehovah’s Witnesses (jw.org). Someone mentioned it on this forum (I can’t find the post anymore though) and I checked it out. Obviously all their writings revolve around one subject. But if you get past this one huge drawback, there seem to be many good things too. It appeared to be a useful site if your main interest is in language elements rather than the subject matter, which is often the case for me.
Since there are interesting new sites coming up all the time, maybe before long we’ll come to a point where lack of resources is never an issue.
Hope you make a good progress, and please don’t hesitate to ask if you have a Korean question for which you can’t find and answer.