И is a vowel, й is a consonant. I'm not a native speaker, but I have pretty good ears and it seems to me that й is considerably shorter than и. They sound like moy and maē, respectively. The o in мой is the only vowel, so it is accented. Мои has two vowels. I'm pretty sure the и is accented, so the o is closer to an a sound.
In English the closest approximation is perhaps: ehtuh knee Tome, ah Moy papa. The o's are kind of like an English long o as in boat, but with the jaw slightly lower. At least it sounds that way to me. listen to a Russian saying vodka to get the idea: Mostly, you need to keep listening to it and parroting it. Also, if you don't know the Cyrillic alphabet definitely learn it. :) https://forvo.com/word/водка/#ru
My guess is that they use these names because they are easier for learners, than if you would use any random Dmitri, Sergey or Vladimir (to give some examples). Tom looks exactly like our alphabet and could be easily read, just like Tim (slight difference with the Russian 'i') so it is an accessible way to learn the Russian alphabet.
I put in "This is not Tom, but my dad" beause i have never heard someone say "but my dad" before and it was wrong. Also, the other time i put "зто не том, а моя папа" and it was wrong -_-. Sometimes i just don't understand proper russian sigh. Help me if you can :D Спасибо!
It's the gender of the thing referred to (not your gender). мой is masculine—masculine nouns usually end with a consonant. й is a consonant. Plurals usually end with ы or и (but some plural nouns end with -a and there are other rarer exceptions), so мои is plural and describes plural things. Most feminine nouns and pronouns end with -a or -я, so you use моя with these. Males always are masculine, regardless of spelling and similarly for females. The most common problem is words ending in -ь. These are male or female and the gender has to be memorized. Still, the gender is easier than in German. Also, neuter is моё. Neuter nouns usually end with -о, -ö, -e, or -ё. The ending -ë is just a stressed -e, but is pronounced more like "yo", so we have "mayó". The two dots are not usually written in most Russian print—only in materials for non-native speakers. These endings are for nominative case. Endings vary in other cases. Welcome to Russian grammar! Ha!
"a" is a conjunction used to contrast two things. In English we can use both "and" and "but" for this purpose: "I am tall and you are short" means the same in English as "I am tall, but you are short." They just have some subtle different feel to them, the second sounding more formal or archaic in some situations. In Russian they would just use "a". So the confusion comes from the fact that in English "and" can be used to mean "but" in some contexts. "a" can be translated as "and" or "but", but it always has the contrasting meaning. In "I'm tall and fat" or " I went to the store and bought groceries." the "and" is "и" not "a" because there is no contrast being implied. I hope that helps.
Sounds very weird to me. Usually, rather used as a conjunction would be followed by a comma and then an independent clause and not a dependent clause: This is not Tom. Rather, it is my dad. What you wrote sounds unnatural to me (in U.S.): The correct translation is something like This is not Tom; this is my dad. To me this sounds more natural than the official Duolingo translation.
You are not entirely wrong. I am an English teacher. I grew up in Texas and live in the West now. This discussion took place in the German course, too. While "but" is not incorrect English grammar it is poor grammar. The proper translation is "but rather" in this sentence. Using either "but" or "rather" alone is unclear and confusing. Used together they provide clarity. Both are accepted in the German course. They should be here, too.
I typed in "This is not Tom, but this is my father", and it is wrong according to the app.
The literal answer it gave me was "This is not Tom, but my dad". Grammatically, it makes no sense, and should otherwise imply that this is his father, not Tom, but it is using the literal translation of the same sentence written in Russian. Report, or no report?
Otherwise, my other thought is that if I were to say "but this is my father" in Russian, it should be at least "а это мой папа".
I found an excellent explanation here: http://learnrussian.rt.com/grammar-tables/conjunctions/