"These are my notebooks."
Translation:Это мои тетради.
Hmmm... Do you know enough German to be familiar with "das ist / das sind"? Even though "das" is also the definite article for neuter nouns, here the same-looking word is used for anything, even plural. It is similar in Russian, but we don't have any word for "is" (or, in German, "ist" or "sind").
You may also find this guide helpful: https://www.duolingo.com/comment/11536858
Oh, this was helpful, thanks!
So if I understand you correctly, one could say that it is 'это' and not 'эти' becausethe the point of the sentence is to clarify that the notebooks are mine, rather than to clarify WHICH notebooks are mine?
If so, if this was the case in English as well, one would say "it are my notebooks" instead of "they/these are my notebooks" when the important information is contained in the word 'my' rather than in 'they'/'these'.
Это is a pronoun in the case of this example and does not inflect to agree with the noun that follows; it takes the base form (which in every language I know is equivalent to masculine singular). Это can also be used as an adjective, in which case it must agree with the noun it modifies. Since we have a feminine plural noun here, это must be made to agree with it, whence эти. Correct?
Not an expert here, but I'll try to explain it according to what I have understood from the Tips and Notes Section. The 7-letter rule applies whenever you have to choose between ы and и. The key is "to choose". In this case, the singular form is тетрадь, which is a feminine noun with a -ь ending. According to the chart in the Tips and Notes Section (plural skill), the feminine nouns that end with the soft sign always make the plural in и. So, in this case, you don't have to choose, it is always the same, and the 7-letter rule doesn't apply here. It does apply in other circumstances, like the feminines (and a few masculines) with а and я endings in the singular (in this case you have to choose between ы and и in the plural according to the 7-letter rule, and most consonant-endings in masculine words. I hope I have helped you.
Oh, don't feel dumb at all. I myself have struggled and I still struggle with so many points of the Russian course. I have taken and left the course several times, and every time I resume the course I feel that I understand a little better than the previous time, so it is just a matter of perseverance, I guess. Bye for now!