To begin with, learn the following: if the subject can be counted and it is combined with the words “one”, “two”, “three”, etc. ( quantitative numerical), then such nouns have singular and plural forms. Accordingly, the singular is to denote one subject, the plural is to denote several (window is windows, river is rivers).
If the subject is uncountable and not used with a quantitative numerical, the name noun with which it is expressed has only the form singular. Such nouns call distracted concepts (dirt, valor), substance or material (gold, water), have a collective meaning (foliage, youth). This includes the names of own (Dnipro, Ural).
Distracted nouns sometimes have a plural form — this gives them a more specific meaning (depth of thought — marine depths, tsarist power — the authorities of the city). Real nouns can also be used in the plural, when denoting certain brands (butter — essential oils) or when the original meaning of the word is changed (street) dirt — medicinal dirt). The plural form the names of their own: when they have a special meaning (Kazanovs, Khlestakovs) or call a group of people who bear the same surname (the Weiner brothers).
Remember that there are nouns that are used only in the plural form. These are nouns calling distracted objects or games (name, hide and seek), paired objects (glasses, pants), time segments (vacation, day), substance (cream, perfume), collective nouns ( finance, debry), as well as proper names, originally of collecting significance (Andes, Gorki). Such nouns sometimes denote considered items, but this is not expressed in the form of a number (Wear new trousers. — The store sells trousers of different sizes.)