In Russian, when you use adjectives (describing words), they need to match the nouns (naming words) in three important ways: gender, number, and case. This means that when you describe something, the words should fit nicely with the nouns you’re talking about.

Let’s break it down:

1. Gender and Cases:

• Nominative Case: This is when you just say something, like "мальчики умные," which means "smart boys."

• Accusative Case: If you say "Я вижу умных мальчиков," it means "I see smart boys." Here, the descriptive word changes a bit because you are talking about what you see.

• Genitive Case: When you say "Нет умных мальчиков," it means "There are no smart boys." Again, the describing word fits with the noun.

2. Plural Formation:

• For regular nouns, like "мальчик" (which means "boy"), the plural form is "мальчики," meaning "boys."

3. Articles:

• In Russian, we do not use words like "the" or "a."

4. Example Sentences:

• "Мальчики высокие" means "The boys are tall."

• "Я люблю умных мальчиков" means "I love smart boys."

Remember, adjectives should always match the nouns they describe in number and case!