In Russian, adjectives, which are words that describe nouns, change based on the nouns they go with. These changes depend on three things:

1. Gender: Is the noun masculine, feminine, or neuter?
2. Number: Is the noun singular (one) or plural (more than one)?
3. Case: What role does the word play in the sentence?

Let’s take the adjective "красивый," which means "beautiful." Here’s how it changes for different genders:

1. Masculine:

   • Singular: красивый
   • Example: красивый мужчина (a beautiful man)

2. Feminine:

   • Singular: красивая
   • Example: красивая женщина (a beautiful woman)

3. Neuter:

   • Singular: красивое
   • Example: красивое здание (a beautiful building)

4. Plural:

   • For all genders, the plural form is: красивые
   • Example: красивые люди (beautiful people)

Comparative Form:
When you want to say something is “more beautiful,” use "более красивый."

• Example: Он более красивый, чем она. (He is more beautiful than she.)

Superlative Form:
To say something is the “most beautiful,” use "самый красивый."

• Example: Это самый красивый город. (This is the most beautiful city.)

Summary:
It's important to match the adjective to the gender and number of the noun. This helps create correct and natural-sounding sentences in Russian.