Translation:It is a kitchen.
The difference between は and が can take a very long time to explain, or fully understand. The simplest way to think about it while you're learning is that は is a topic marker. It says "this is what I'm talking about". が is a subject marker, and can convey that you're giving the listener/reader information that wasn't already known to them.
が directs what is after it towards whats before it. は, from what i understand emphasizes whats after it. Ex: "いすが一つあります。" "There is one CHAIR." I think the alternative is something like "The chair is one." Which can be used when playing a game with friends where you point out wooden objects...but im not a pro so...(xp)
Both これ and ここ (meaning "this place") are acceptable translations depending on the situation you are in.
If you are already in the kitchen, ここ is the better choice. If you are just outside, or pointing to the kitchen on a map, then これ is probably more common, but not necessarily more correct.
これ means this/this one (near listener)
それ means that/that one (near listener)
あれ means that/that one/that one over there (far from speaker and listener)
この+N means this (near speaker and comes before nouns)
その+N means that (near listener and comes before nouns)
あの+N means that/that one (far from speaker and listener and comes before nouns)
ここ means here (near speaker)
そこ means there (near listener)
あそこ means there/over there ( far from speaker and listener)
Kanji is simpler, if you know kanji. If not, then it's significantly more complicated.
Also, I agreed it should be accepted, but saying Duo is being difficult and picky is a bit unfair. The Japanese course is (still) in Beta, so bugs like things being marked incorrect when they should be correct or vice versa are still being ironed out. (Disclaimer: I'm not one of the course developers, so please don't take my opinion to be representative of theirs.)