Capital letters, also known as uppercase letters, are used in specific situations in English writing. Here are some common rules for when to use capital letters:

1. Sentence Beginnings: Capitalize the first letter of the first word in a sentence. Example: The sun is shining brightly.
2. Proper Nouns: Capitalize the first letter of proper nouns, which are specific names of people, places, organizations, or things. Example: Mary, London, Google, Eiffel Tower
3. Titles and Headings: Capitalize the first letter of each major word in titles and headings, including books, articles, essays, blog posts, and headings within documents. Example: The Great Gatsby, How to Write an Effective Blog Post
4. Names and Titles: Capitalize the first letter of a person’s name and their title when used as part of their name. Example: President Obama, Professor Johnson
5. Days of the Week, Months, and Holidays: Capitalize the names of days of the week, months, and holidays. Example: Monday, December, Christmas
6. Geographic Names: Capitalize the names of countries, cities, states, streets, rivers, mountains, and other geographic locations. Example: Brazil, New York City, Mississippi River
7. Initials and Acronyms: Capitalize all the letters in initials and acronyms. Example: NASA, CEO, HTML
8. Historical Events and Periods: Capitalize the names of historical events, eras, and significant time periods. Example: World War II, the Renaissance
9. Brand Names: Capitalize the names of brands, products, and companies. Example: Nike, iPhone, Coca-Cola
10. Titles of Works: Capitalize the principal words in the titles of books, movies, songs, poems, and other creative works. Example: To Kill a Mockingbird, Bohemian Rhapsody

It’s important to note that capitalization rules may vary in specific contexts or writing styles. Additionally, it’s generally recommended to avoid excessive capitalization, such as capitalizing common nouns or random words within a sentence, as this can be considered incorrect or poor writing style.