English nouns can be ‘countable’ and so have both singular and plural forms, or they can be ‘uncountable’, in which case they only have the singular form.
Countable nouns are usually preceeded by an article or a quantity:
a cat – two cats
Uncountable nouns tend to have general or abstract meanings:
The verb conjugation is always singular with uncountable nouns:
Wine is good in Italy.
You can indicate the quantity of an uncountable noun like this:
Two glasses of wine
Three kilos of flour
Students often make mistakes with words which may be countable in their own language but which are uncountable in English, for example:
My homework is easy.
Money is not important for him.
On the other hand, “people” is usually plural:
People in Japan are very hospitable.