What are the rules for using possessive nouns in grammar?

The rules for using possessive nouns in grammar are as follows:

1. Singular Possessive Nouns: To show ownership or possession of a singular noun, add an apostrophe (') followed by an "s" at the end of the noun. For example:
- The dog's bone
- John's car
- The book's cover

2. Plural Possessive Nouns: To show ownership or possession of a plural noun, if the noun already ends with an "s," simply add an apostrophe (') at the end. If the plural noun does not end with an "s," add an apostrophe (') followed by an "s" at the end. For example:
- The dogs' bones
- The students' books
- The children's toys

3. Possessive Nouns with Irregular Plurals: Some nouns have irregular plural forms, and to show possession, the same rules apply. For example:
- The men's hats
- The women's shoes
- The children's clothes

4. Joint Possession: When two or more people share ownership of something, only the last noun takes the possessive form. For example:
- John and Mary's house (the house belongs to both John and Mary)
- The company's employees (the employees belong to the company)

5. Indefinite Pronouns: When using possessive pronouns like "someone," "anyone," or "everyone," add an apostrophe (') followed by an "s" to show possession. For example:
- Someone's bag
- Anyone's guess
- Everyone's opinion

6. Compound Nouns: When using compound nouns, only the last word takes the possessive form. For example:
- My sister-in-law's car
- The attorney general's office

Remember to use possessive nouns to indicate ownership or possession in a sentence. These rules will help ensure correct usage of possessive nouns in grammar.