It is difficult to explain the different case, in English the difference is seen with the help of prepositions, but there are no pretexts here.
In Russian, in order to distinguish between cases, these questions raise different questions and auxiliary words, (accusative case) I see vody, I drink vody - я вижу воду, я пью воду (что?) Give me vodУ Дай мне (что?) воду нет воды, нет мамы, нет кошки - ( оf чего, кого?)(родительный падеж) (genitive) But you can say give me водЫ ( of what) (drink) questions of what and what are not the same thing
-у/-ю is the accusative ending for singular feminine words ending in -а/-я. Use the accusative case when the noun is the direct object (the thing being acted on directly, like if you're throwing a ball, ball is the direct object) or when it's a the destination of motion (for instance, станция - я иду на станцию).
-и/-ы is the genitive singular ending for singular feminine words. Genitive is used to describe the absence or negation of something (у меня нет воды); to describe the relationship between two things or people (машина моей мамы - my mom's car, literally: the car of my mom); with the numbers 2, 3 and 4 (две машины, четыре кошки, сорок три кошки [43 cats]), etc.
Kind of a crash course explanation, I recommend using other online resources to study Russian cases and their rules.
"ё" (ye) is a rare letter. So you can break your tongue ё. You can write e, but you only need to say “ё”,
these are the words with "ё" : Лёд, мёд, идёт, поёт, берёт, вперёд, ёж, ёлка, ёлки-палки, несёт, прилёт, Ice, honey, goes, sings, takes, forward, hedgehog, Christmas tree (spruce), carries, arrives, And in the same root words - н "ё"с, л"ё"т, carried fly away
Mostly. According to the wiki article, the only times it doesn't is in words imported from roman alphabets, to represent a consonant "Y" (е.g., "New York" : Ню-Йорк).
But that's fussy, and I suspect that the only-after-vowels rule will apply to everything we deal with here on Duolingo (like мой, твой, and американский thus far).