This is the 1230th most frequent Russian word.
мой
"My" translates to "my" or "mine" in English, indicating possession.
In this sentence, 'мой' is a possessive pronoun used to modify a masculine noun in the nominative case.
Это мой друг.
This is my friend.
Here, 'мою' is the feminine accusative form of the possessive pronoun 'мой', agreeing with the direct object 'книгу'.
Ты видел мою книгу?
Did you see my book?
In this case, 'мои' is the plural form of the possessive pronoun 'мой', modifying a plural noun in the accusative case.