There are tips and notes for every lesson, but they are only visible in the web app. https://www.duolingo.com/skill/ru/Possessive-Modifiers-1
Tips and notes
POSSESSIVE ENEMY MINE
There isn't much to say about words like "my" or "your" in Russian.
his/her/their do not change: его́, её, их(and they don't get an initial Н after prepositions!)
my/your/our roughly follow an adjectival pattern, i.e. they copy the gender and the case of the noun they describe. Just like этот:
Unlike English, no distinction is made between my and mine, her and hers etc.
Pronunciation: in «его», as well as in adjective endings and "сегодня" the letter Г is pronounced В. It is a historical spelling.
Nouns in Russian belong to one of three genders: feminine, masculine or neuter. If a noun means a person of a certain gender, use that one. For all other nouns look at the end of the word:
(TABLE) ENDING IN NOM; GENDER; EXAMPLES
-а/-я ; feminine ; ма́ма, земля́, Росси́я, маши́на
consonant ; masculine ; сок, ма́льчик, чай, интерне́т, апельси́н
-о/-е ; neuter ; окно́, яйцо́, мо́ре
-ь ; feminine or masculine - consult a dictionary ; ло́шадь, ночь, мать, любо́вь / день, конь, медве́дь, учи́тель
IF THERE'S A SOFT SIGN, IT ISN'T POSSIBLE TO PREDICT THE GENDER, AT LEAST, NOT ACCURATELY. HOWEVER, ABOUT 65-70% OF THE MOST USED NOUNS THAT END IN -Ь ARE FEMININE. ALSO, YOU CAN LEARN THE COMMON SUFFIXES ENDING IN A SOFT SIGN THAT PRODUCE A WORD OF A PREDICTABLE GENDER. THEY ARE:
-ость/-есть, -знь → feminine
-тель, -арь, -ырь → masculine
ALL NOUNS WITH -ЧЬ, ЩЬ, -ШЬ, -ЖЬ AT THE END ARE FEMININE. THE CONVENTION IS TO SPELL FEMININE NOUNS WITH A SOFT SIGN AND MASCULINE ONES WITHOUT ONE: НОЖ, ЛУЧ, МУЖ, ДУШ. IT DOESN'T AFFECT PRONUNCIATION, ANYWAY.
No, a dash is not required here. We put dashes when both the subject and the predicate are nouns, or when subject is noun and the predicate is infinitinve, or in some other cases (here, in Russian), but in this sentence we don't have any reasons to put it.
However, the dash is probably the least codified punctuation mark, and many people just place it almost anywhere to mark a pause. Some writers are notorious for abusing dashes. There's a joke «Нельзя! Нельзя — учиться пунктуации по — Цветаевой!» (You can't! You can't — learn punctuation from — Tsvetayeva!) which makes fun of Tsvetayeva's creative use of dashes.
So if you place a dash here, it won't really be a mistake. You can probably place a dash anywhere.
That would place the emphasis on кошка (in Russian, the most important, new piece of information goes at the end, and the old information at the beginning), and not on the fact that it is ours. So that would be more like "This is our cat" (For example, telling the listener that we have a cat, when they previously did not know that there was a cat at all). The given sentence places the emphasis on наша, that is, the fact that it is our cat (for example if the listener had found the cat and asked "Hey, who is responsible for this cat?").