Translation:I go far away.
I'm not sure what you are saying. But there are two groups of adjectives in Japanese. One is group is commonly called 'i' adjectives or "true" adjectives and usually end in -ai, -ii, -ui, -oi - some examples - akai - red, subarashii - wonderful, samui - cold, kuroi - black. 'i' adjectives can modify the nouns that they describe directly - they don't need any help eg. samui hi - cold day, akai boushi - red hat, subarashii geemu - wonderful game, kuroi inu - black dog. The other group of adjectives are called 'na' adjectives and they need 'na' to help them modify the nouns that they describe - some of them even look like they might be 'i' adjectives like kirei - but don't be fooled! Some examples - shizuka, kirei, suteki, rippa. shizuka na kodomo - quiet child, kirei na niwa - pretty garden, suteki na shaatsu - cool/smart shirt, rippa na sensei - great teacher.
Japanese adjectives can be made into adverbs. Adverbs describe verbs or in other words how an action is performed - quickly, slowly, quietly. To make 'i' adjectives into adverbs you remove the final 'i' and add ku - hayai - quick becomes hayaku - quickly, yasashii - kind becomes yasashiku - kindly/gently. To make 'na' adjectives into adverbs you replace na with ni. Shizuka na - quiet becomes shizuka ni - quietly, kirei na - clean becomes kirei ni - cleanly.
To continue AnaLydiate's excellent explanation, since you asked about negation: if you want to say that something isn't X, you again need to know if it is an i-adjective on a na-adjective. With i-adjectives, you change the -i to -kunai: inu wa kurokunai desu "The dog is not black." With na-adjectives you instead use the negative form of the verb: niwa wa kirei de arimasen "The garden is not pretty."
If you read the other comments and do a quick search on jisho.org, you can see that this can actually be used as an adverb AND a noun, unlike other adjectives that are changed into the adverb form. Here, it is used as a noun, as KeithWong9 has already said. This is a confusing and weird sentence that Duolingo has used which does not make sense given the various other questions this lesson gives.
*Please upvote this comment so others can see
First of all, it is an affirmative sentence. For commanding others it would be 遠くに行ってください/遠くに行きなさい/遠くに行け with decresing degree of politeness. It is rude to say so even for the first one however, and it does not quite convey the meaning of go away.
We use 帰（かえ）る normally as in 帰ってください. A more polite one would be お引（ひ）き取（と）りください.
Rude ones include 失（う）せろ, 帰（かえ）れ. Don't say these to others :-)
I doubt "I are going to go far way" was ever considered a correct translation - the English is incorrect. "are" is the wrong form of "to be" to go with "I". There's nothing wrong with the current English translation. If we were going to pick at anything it would be that Duo should really also accept I go far as well. I AM going to go far away is also acceptable.
piguy - I thought you were referring to the translation at the top of the page. You are right - Duo's "correction" here is wrong. Also thought we couldn't post images in the comments - hooray for progress! This'll clear up a lot of things because I've often suspected that different Duo users see different things in the lessons - not sure if it is because of the devices being used or browsers on computers but from the comments made it sure looks like we don't always all see the same things in Duo lessons - or at least their Japanese lessons.
Yeah, I reported it (both the correct version and that there's an error in what's there now), but having read threads from contributors mentioning that the "Correct answer contains an error" option is too ambiguous to help them (Unsurprisingly, since it doesn't let them know what "correct" answer contains the problem out of the possibly thousands in the system), I also posted here.