Translation:I do not like meat.
They use は to introduce the topic of the sentence. Whereas, が could be confusing because is like you are responding a question. For example, What do you like? I like meat (が). You use が because you have to bare in mind that the other person didn't know the subject of that sentence before and therefore you need to use that particle.
Keeping the です makes it more polite like the ~ます form of verbs. You would only use じゃない, commonly referred to as plain form, when talking with children/someone younger than you, friends, family (younger siblings), or こうはい (someone in a junior or inferior position to you at work) - if you want to be polite. Some people don't see the point and talk to everyone in plain form - although they might not say so, this would be considered really rude!
This app is disappointing is it wasnt for the comments i would have giving up i feel bad if this app was ppl's first intro to Japanese because there r so many key component that r not even stressed like politeness levels and particle's and radicals for kanji that help make learning easier that arent even focused on.
Perhaps your expectations were set a bit too high. If you try any of Duolingo's other courses, you'll see they all function in much the same way. Two main reasons this isn't so disappointing:
Firstly, Duo is not about actual, substantial courses for properly acquiring new languages. It's just a free-to-use website/app, that can help you with learning and/or maintaining some languages. They're fun, quick, and easy little vocab builders, with just enough grammar to get by.
Secondly, the Japanese course is new and currently only has a functional app version, which doesn't feature explanations found in web versions. My guess is that those are being worked on, and will be made available when ready. I'm sure the length (i.e.g number of lessons/topics) of the course will be increased in due time too. Plus, Japanese is quite different from all the other languages currently on offer by Duo, so some adaption issues may be expected.
My advice for anyone who wants to get serious about any language; pick up a book and/or take a class, and think of Duo as a bonus.
The course is in Beta. I have watched other courses released in Beta improve dramatically in the process of becoming full courses (Russian is a great example of this); in fact I've been surprised how many changes I've seen in the first week of Japanese being released on Desktop, so I'm hopeful that it will continue to improve.
I also notice your comment is from a month back; I'd encourage you to try the course on web/Desktop. You can learn a ton more, because it has open-ended typing exercises. Also, with an input method, it's much easier to learn Kanji that aren't explicitly taught, and you can test yourself on them by typing them into the answers and seeing if they're correct.
When I studied Japanese before (using a book, not duo), I was presented with two forms: ではない and ではありません. Later I learned about じゃ, which means では, but never have I seen じゃないです.
I remember explicitly learning that there are two types of adjectives in Japanese: い-adjectives and な-adjectives. The first one are followed exclusively by です or nothing, which means that the past and negative forms of, for example, うれしい are respectively: うれしかった（です） and うれしくない（です）. The second form however is constant and です is the one who changes when the sentence is negative and/or in past tense, as well as it's the one who assumes the appropriate form given the level of politeness intended: 好きじゃない/ではありません and 好きだった/でした.
My point is, in this case it seems as though 好き was treated as a い-adjective instead of a な-adjective, but the comments suggest that the sentence is correct and that です can indeed be used like that. Is that really correct? Am I missing something now or misinterpreting something from my previous Japanese studies?
Short answer: This sentence is natural, though strictly speaking it was not originally correct.
Well, I must say that you study grammar books very hard, but sometimes grammar books aren't consistence with daily conversation.
First, 好き is always a な- adjective, you didn't get it wrong. Second, the "be" in Japanese is originally like this:
informal negative: -ではない
formal/ polite negative: -ではありません
the い adjectives are originally like this:
informal negative: -うれしくない
formal/ polite negative: -うれしくありません
But many Japanese started to combine informal negative form with です and becoming ではないです or うれしくないです- it is not as formal as ではありません, but not as impolite as ではない. I think that might be because some people say informal -ない but suddenly recognize that he or she should be more polite so he or she just add -です after it. (Just guessing, though)
Even when I went to Japan this year I found that most Japanese people use -ないです, and some grammar books start to tell you that ではないです is very natural, which was said to be incorrect years ago.
This woman has been complaining about the food all lessons, even saying at one point she doesn't like water.
I'm thinking it's a 101 case of veganism but eagerly await a phrase where she says she doesn't like vegetables to confirm it's actually a breatharian talking - the ultimate natural diet to opt-out of life xD