Translation:You are wrong; that city is in Poland.
There are about 17 different forms unless you count the singular and plural forms separately, which would nearly double them, and then you could triple them if you add comparative and superlative forms into the mix, so it would take a while to go through all of them individually. The more relevant thing to focus on are grammatical cases because that cuts to the crux of the matter. For example, "väärän" has either genitive case or accusative case, and "väärässä" has inessive case. But "väärin" is usually an adverb, so grammatical case doesn't apply to it (when it's an adverb). Grammatical cases are applied to all Finnish nominals, which are nouns, pronouns, adjectives, and numerals. Adverbs are not included in that list. Knowing when to use each form is as simple and complicated as knowing when to use each grammatical case.
Because of the inessive case, "väärässä" literally means "in the wrong", and while that can also work as a proper translation, it's usually translated to just "wrong", like in the sentence above this thread. The genitive case in "väärän" literally means "of the wrong". An example where the genitive form could be used is "väärän kissan karvat", meaning "the fur of the wrong cat". Accusative case has two forms for most nominals; one that is identical to nominative case and another that is identical to genitive case, which is why "väärän" can also be in accusative case. The nominative-accusative form is mostly used when the verb is imperative or passive, and the genitive-accusative form is almost always used in other situations. Accusative case is used to indicate the total object of an action, similarly to how "him" indicates that a "he" is the object of an action. An example would be "sain väärän tuotteen", meaning "I received a/the wrong product". But note that the object can also be in partitive case when the action is irresultative or ongoing. The partitive form would be "väärää".
The adverb "väärin" is used whenever you would use "wrong" as an adverb, for example "you did that wrong", but also additionally in predicative expressions about a factual or moral wrongness, where the English equivalent would be an adjective, like "violence is wrong", which would be "väkivalta on väärin" in Finnish. Then there's also possessive forms for 1st person, 2nd person, and 3rd person, of which all but the latter has both a singular and a plural form, but those are rare because it's hard to imagine situations where one could own "a wrong".
Anyway, the point is that you'll figure it out by figuring out grammatical cases. They have roles that are often covered in English by prepositions, but it would be dead wrong to assume that each case is perfectly equivalent to a specific English preposition. You may find this helpful in getting started: https://en.wikipedia.org/wiki/Finnish_noun_cases
Trying to learn Finnish by memorising every word is doomed to fail as Kristain suggests. Rather determine whether a word is
- a verb
- a nominal
- an adverb
In case of a nominal try to determine its case, because that gives you an idea about the word's role in the sentence.
Let's analyse the first part of the sentence in this exercise: Olet väärässä.
- Olet : the verb "to be" is perhaps the most common one, you recognise that this is the singular second person form of olla, so we are talking about something "you are"
- väärässä : ok, this ends in -ssa/ssä which often corresponds to the preposition "in"; since there is no k, l, t or p in the stem (but r), it's safe to assume that no consonante alternation has taken place, so väärä is the singular nominative form
If you don't remember what väärä means, check in a dictionary and you find "(adj.) wrong" . So the sentence is "you are in wrong", which might not be the most idiomatic way to say it in English, but it's close enough for you to understand.
But now you learnt that väärä is an adjective and therefore you can use it as an adjective attribute for total objects, Minulla on väärä paita and partial ones, Seurasin väärää profeettaa. You probably easily learn to form an adverb from it: Teinkö jotain väärin?
Fight it out! Good luck!
You must report your answer as "my answer should be accepted" if you want the development team to get notified about it.
Having said that I am not sure – being a non-native speaker of English – but I think it should not be accepted. A person can be wrong when their answer is incorrect, i.e. you use "wrong" about when a human errs or a matter is morally unjustifiable, "incorrect" is about an answer, a reply, a statement or similar and which is erroneous.
You are not alone. On another course here in Duolingo this same question came up. It seems that in USA "a city" denotes an administrative unit and has nothing to do with the size, so every god-forsaken cluster of buildings can be "a city". Everywhere else "a city" is a big urban area and "a town" a small urban area.
When it comes to Finnish, the normal word is kaupunki for all sizes. If you say suurkaupunki, then you are emphasising the size. My free translation example:
- Suurkaupunki Tokiossa asuu yli 36 miljoonaa ihmistä. Kaupungin alueeseen kuuluu varsinaisen metropolin lisäksi lukuisia prefektuureja : In the city of Tokyo there are over 36 million inhabitants. Besides the metropolitan area severel prefektures are part of the greater city area.
Thank you for making me smile with your "isokaupunki." Never seen that before. In Finnish, we usually use just kaupunki for both city and town.
Sometimes I use "town" to refer to the center of a rural municipality in Finland because I haven't found a better word for it. Suurkaupunki is more likely in Finnish than "isokaupunki" but I rarely use it. Maybe because it's not relevant in my everyday life, as the scale is smaller here and I don't think there are any "suurkaupunki" in Finland.