how can you tell between genders in the words?

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1. Look at the last letter of the word:
2. If it is a consonant, or “й”, the word is masculine.
3. If it is “а” or “я” it is feminine.
4. If it is “о” or “е” it is neuter.
5. If it is a soft sign “ь” then it could be either masculine or feminine.
There are very few exceptions to these rules. But there are five notable exceptions, this occurs mainly because of physical gender.
Папа - (Daddy, Papa) - Is Masculine
Дядя - (Uncle) - Is Masculine
Дедушка - (Grandfather) - Is Masculine
Мужчина - (Man) - Is Masculine
Кофе - (Coffee) - Is Masculine
Some examples:
Masculine : паспорт (passport), документ (document), брат (brother), Хлеб (bread).
Feminine : газета (newspaper), Россия (Russia), Дочь (daughter)
Neuter : здание (building), радио (radio), письмо (letter)