Noun theory in Belarusian grammar focuses on understanding the various aspects of nouns and their usage in the language. Nouns in Belarusian can be categorized into different genders: masculine, feminine, and neuter. They also have various cases, such as nominative, genitive, dative, accusative, instrumental, and prepositional, which determine their functions in sentences.

Nouns in Belarusian also have singular and plural forms, with rules for their formation. The formation of plurals is based on different patterns and irregularities that need to be studied and memorized.

Another important aspect of noun theory is the declension of nouns, which involves changing the endings of the nouns depending on their grammatical function in a sentence. This can be influenced by the gender, number, and case of the noun.

Understanding noun theory is crucial for developing proficiency in Belarusian grammar. It helps learners to correctly form sentences, use appropriate noun endings and declensions, and effectively communicate in the language.