"These are apples."
Translation:ये सेब हैं।
It can be 'They are apples' as well.
However, 'Those are apples' would be 'वे सेब हैं'.
Apple/apples and man/men are the same words - is there any rule for knowing this, or is it just like English sheep and fish, just something to learn and remember?
It's just like the English sheep and fish. You can look at the verb that is conjugated with the noun to make out whether it is singular or plural. Singular सेब would go with है while the plural सेब would go with a हैं.