Translation:It has really been a long time.
Literal translation: "really long time". Durolingo translation: "It has really been a long time." There are four extra words. At some time Durolingo needs to explain where these extra words came from.
Different languages need different words (and extra words sometimes) to explain the same concepts, which is why literal translations don't always work.
The English sentence requires an indefinite article to work (a long time), whereas the Korean language doesn't even have one. The English sentence also needs the present perfect progressive to express the idea of an ongoing action (it has been), which, again, the Korean language doesn't have, so it uses the present tense instead (입니다). The nuance of the present perfect progressive is lost in the Korean sentence, but so is the nuance of the level of formality lost in the English sentence, because some translations will never be word-for-word accurate, so you shouldn't treat them as such.
정말(正=true + 말=word) = really/truly
오랜 = a long time
만 = after/again/the first time in ~ [This is complicated to say the least so it's just one of its many uses, in this case as a dependent nominal rather than a particle and so separated by an initial space, except it isn't in this particular compound word. Basically, help!]
입니다! = it's
So as close as I can get to literally, "It's the first time in really a long time."