Using capital letters
You should always use a capital letter in the following situations:
In the names of people, places, or related words
Use a capital letter when you are writing the names of people, places, and words relating to them:
At the beginning of a sentence
Use a capital letter at the beginning of a sentence:
The museum has huge potential. It will be a great boost to the area and we are really excited about it.
In the titles of books, movies, organizations, etc.
Use a capital letter in the titles of books and other publications, movies, organizations, special days, etc. In such cases, you need a capital letter for all the main words but not for the connecting words such as a, an, the, or, and, etc.:
Pride and Prejudice
the House of Representatives
If you’re using the first letter of the abbreviated words, every letter should be a capital, even if the abbreviated words are not normally capitalized, e.g.:
NBC (National Broadcasting Company)
USA (United States of America)
BMI (body mass index)
See more about writing abbreviations.
People often don’t use capital letters when they’re writing e-mails or other informal messages, but it’s important to follow the rules above in formal writing.